全文获取类型
收费全文 | 5141篇 |
免费 | 313篇 |
国内免费 | 4篇 |
专业分类
5458篇 |
出版年
2023年 | 17篇 |
2022年 | 35篇 |
2021年 | 49篇 |
2020年 | 38篇 |
2019年 | 52篇 |
2018年 | 84篇 |
2017年 | 82篇 |
2016年 | 101篇 |
2015年 | 182篇 |
2014年 | 211篇 |
2013年 | 343篇 |
2012年 | 309篇 |
2011年 | 369篇 |
2010年 | 211篇 |
2009年 | 172篇 |
2008年 | 309篇 |
2007年 | 347篇 |
2006年 | 315篇 |
2005年 | 331篇 |
2004年 | 281篇 |
2003年 | 286篇 |
2002年 | 267篇 |
2001年 | 79篇 |
2000年 | 59篇 |
1999年 | 79篇 |
1998年 | 75篇 |
1997年 | 55篇 |
1996年 | 63篇 |
1995年 | 55篇 |
1994年 | 33篇 |
1993年 | 42篇 |
1992年 | 49篇 |
1991年 | 32篇 |
1990年 | 38篇 |
1989年 | 41篇 |
1988年 | 31篇 |
1987年 | 33篇 |
1986年 | 25篇 |
1985年 | 29篇 |
1984年 | 39篇 |
1983年 | 27篇 |
1982年 | 32篇 |
1981年 | 17篇 |
1980年 | 24篇 |
1979年 | 16篇 |
1978年 | 10篇 |
1977年 | 12篇 |
1976年 | 9篇 |
1974年 | 11篇 |
1973年 | 9篇 |
排序方式: 共有5458条查询结果,搜索用时 15 毫秒
991.
Kosuke Nakanishi Takayoshi Nishida Masahiro Kon Hiroichi Sawada 《Entomological Science》2014,17(2):251-261
Although irrigation ponds contribute to the conservation of aquatic biodiversity, they have experienced declines in recent years. We therefore examined the relationships between various environmental factors and the community composition of aquatic insects, specifically insect predators, in irrigation ponds to gain knowledge that would aid in the conservation and restoration of biodiversity. We selected Odonata, Hemiptera and Coleoptera as target taxonomic groups and conducted censuses of these groups in 21 ponds in Shiga, central Japan. In total, we collected 30 and 10 species (or species groups) of Odonata and Hemiptera, respectively, and 17 species of Coleoptera. A partial canonical correspondence analysis revealed that the following four environmental factors significantly affected the species composition of aquatic insect communities: the number of emergent plant species, percent concrete revetment, presence of litter and peripheral length. Among these variables, the number of emergent plant species was the most potent factor, perhaps because emergent plants serve as sites for oviposition and emergence, and provide refugia for aquatic insects (odonate nymphs in particular). In contrast, some species specifically inhabited sites poor in emergent plants. This study shows that reductions in concrete revetments are necessary for the conservation of biodiversity. This would lead to increases in the number of aquatic plant species, which provide habitats and oviposition sites for many aquatic insects. Furthermore, to enrich the local biodiversity of aquatic insects, groups of irrigation ponds with different environments are needed. 相似文献
992.
Hironori Kakoi Shingo Maeda Naohiro Shinohara Kanehiro Matsuyama Katsuyuki Imamura Ichiro Kawamura Satoshi Nagano Takao Setoguchi Masahiro Yokouchi Yasuhiro Ishidou Setsuro Komiya 《The Journal of biological chemistry》2014,289(12):8135-8150
Although bone morphogenic protein (BMP) signaling promotes chondrogenesis, it is not clear whether BMP-induced chondrocyte maturation is cell-autonomously terminated. Loss of function of Smpd3 in mice results in an increase in mature hypertrophic chondrocytes. Here, we report that in chondrocytes the Runx2-dependent expression of Smpd3 was increased by BMP-2 stimulation. Neutral sphingomyelinase 2 (nSMase2), encoded by the Smpd3 gene, was detected both in prehypertrophic and hypertrophic chondrocytes of mouse embryo bone cartilage. An siRNA for Smpd3, as well as the nSMase inhibitor GW4869, significantly enhanced BMP-2-induced differentiation and maturation of chondrocytes. Conversely, overexpression of Smpd3 or C2-ceramide, which mimics the function of nSMase2, inhibited chondrogenesis. Upon induction of Smpd3 siRNA or GW4869, phosphorylation of both Akt and S6 proteins was increased. The accelerated chondrogenesis induced by Smpd3 silencing was negated by application of the Akt inhibitor MK2206 or the mammalian target of rapamycin inhibitor rapamycin. Importantly, in mouse bone culture, GW4869 treatment significantly promoted BMP-2-induced hypertrophic maturation and calcification of chondrocytes, which subsequently was eliminated by C2-ceramide. Smpd3 knockdown decreased the apoptosis of terminally matured ATDC5 chondrocytes, probably as a result of decreased ceramide production. In addition, we found that expression of hyaluronan synthase 2 (Has2) was elevated by a loss of Smpd3, which was restored by MK2206. Indeed, expression of Has2 protein decreased in nSMase2-positive hypertrophic chondrocytes in the bones of mouse embryos. Our data suggest that the Smpd3/nSMase2-ceramide-Akt signaling axis negatively regulates BMP-induced chondrocyte maturation and Has2 expression to control the rate of endochondral ossification as a negative feedback mechanism. 相似文献
993.
Yusuke Shibafuji Akihiko Nakamura Takayuki Uchihashi Naohisa Sugimoto Shingo Fukuda Hiroki Watanabe Masahiro Samejima Toshio Ando Hiroyuki Noji Anu Koivula Kiyohiko Igarashi Ryota Iino 《The Journal of biological chemistry》2014,289(20):14056-14065
Trichoderma reesei cellobiohydrolase I (TrCel7A) is a molecular motor that directly hydrolyzes crystalline celluloses into water-soluble cellobioses. It has recently drawn attention as a tool that could be used to convert cellulosic materials into biofuel. However, detailed mechanisms of action, including elementary reaction steps such as binding, processive hydrolysis, and dissociation, have not been thoroughly explored because of the inherent challenges associated with monitoring reactions occurring at the solid/liquid interface. The crystalline cellulose Iα and IIII were previously reported as substrates with different crystalline forms and different susceptibilities to hydrolysis by TrCel7A. In this study, we observed that different susceptibilities of cellulose Iα and IIII are highly dependent on enzyme concentration, and at nanomolar enzyme concentration, TrCel7A shows similar rates of hydrolysis against cellulose Iα and IIII. Using single-molecule fluorescence microscopy and high speed atomic force microscopy, we also determined kinetic constants of the elementary reaction steps for TrCel7A against cellulose Iα and IIII. These measurements were performed at picomolar enzyme concentration in which density of TrCel7A on crystalline cellulose was very low. Under this condition, TrCel7A displayed similar binding and dissociation rate constants for cellulose Iα and IIII and similar fractions of productive binding on cellulose Iα and IIII. Furthermore, once productively bound, TrCel7A processively hydrolyzes and moves along cellulose Iα and IIII with similar translational rates. With structural models of cellulose Iα and IIII, we propose that different susceptibilities at high TrCel7A concentration arise from surface properties of substrate, including ratio of hydrophobic surface and number of available lanes. 相似文献
994.
Masakazu Ishii Rei Shibata Kazuhisa Kondo Takahiro Kambara Yuuki Shimizu Tohru Tanigawa Yasuko K. Bando Masahiro Nishimura Noriyuki Ouchi Toyoaki Murohara 《The Journal of biological chemistry》2014,289(39):27235-27245
Dipeptidyl peptidase-4 inhibitors are known to lower glucose levels and are also beneficial in the management of cardiovascular disease. Here, we investigated whether a dipeptidyl peptidase-4 inhibitor, vildagliptin, modulates endothelial cell network formation and revascularization processes in vitro and in vivo. Treatment with vildagliptin enhanced blood flow recovery and capillary density in the ischemic limbs of wild-type mice, with accompanying increases in phosphorylation of Akt and endothelial nitric-oxide synthase (eNOS). In contrast to wild-type mice, treatment with vildagliptin did not improve blood flow in ischemic muscles of eNOS-deficient mice. Treatment with vildagliptin increased the levels of glucagon-like peptide-1 (GLP-1) and adiponectin, which have protective effects on the vasculature. Both vildagliptin and GLP-1 increased the differentiation of cultured human umbilical vein endothelial cells (HUVECs) into vascular-like structures, although vildagliptin was less effective than GLP-1. GLP-1 and vildagliptin also stimulated the phosphorylation of Akt and eNOS in HUVECs. Pretreatment with a PI3 kinase or NOS inhibitor blocked the stimulatory effects of both vildagliptin and GLP-1 on HUVEC differentiation. Furthermore, treatment with vildagliptin only partially increased the limb flow of ischemic muscle in adiponectin-deficient mice in vivo. GLP-1, but not vildagliptin, significantly increased adiponectin expression in differentiated 3T3-L1 adipocytes in vitro. These data indicate that vildagliptin promotes endothelial cell function via eNOS signaling, an effect that may be mediated by both GLP-1-dependent and GLP-1-independent mechanisms. The beneficial activity of GLP-1 for revascularization may also be partially mediated by its ability to increase adiponectin production. 相似文献
995.
Takashi Sakurai Anthony Lanahan Melissa J. Woolls Na Li Daniela Tirziu Masahiro Murakami 《Journal of visualized experiments : JoVE》2014,(88)
Primary rat neonatal cardiomyocytes are useful in basic in vitro cardiovascular research because they can be easily isolated in large numbers in a single procedure. Due to advances in microscope technology it is relatively easy to capture live cell images for the purpose of investigating cellular events in real time with minimal concern regarding phototoxicity to the cells. This protocol describes how to take live cell timelapse images of primary rat neonatal cardiomyocytes using a confocal spinning disk microscope following lentiviral and adenoviral transduction to modulate properties of the cell. The application of two different types of viruses makes it easier to achieve an appropriate transduction rate and expression levels for two different genes. Well focused live cell images can be obtained using the microscope’s autofocus system, which maintains stable focus for long time periods. Applying this method, the functions of exogenously engineered proteins expressed in cultured primary cells can be analyzed. Additionally, this system can be used to examine the functions of genes through the use of siRNAs as well as of chemical modulators. 相似文献
996.
QU Le-Qing WEI Xiao-Li SATOH Hikaru OGAWA Masahiro KUMAMARU Toshihiro 《植物学报(英文版)》2001,43(11):1167-1171
Nine rice Oryza sativa L.) mutant lines lacking the seed storage glutelin α-2 subunit were obtained from the progenies of fertilized egg cells treated with N-methy-N-nitrosourea (MNU). The mutants could be classified into three types: the α-1 subunit increased type (α-1H/α-2L), decreased the β-2 subunit decreased type (β-2L/α-2L) and the α-3 subunit increased type (α-3H/α-2L) according to their SDS-PAGE profiles. Two-dimensional electrophoresis analysis revealed that all of the mutants lacked a polypeptide of pI 6.71/α-2, while new polypeptides of pI 6.50/α-1 and pI 6.90/α-3 formed in α-1H/α-2L and α-3H/α-2L mutants respectively. Although the β-2L/α-2L mutants did not form new polypeptide, their pI 8.74/β-2 polypeptide was also decreased, suggesting that the two polypeptides decreased in β-2L/α-2L mutants might derive from the same glutelin precursor. These mutant lines are very useful in studying genetic characterisation,the mechanism of genetic regulation on biosynthesis, gene function and proteomics of rice seed storage glutelin. 相似文献
997.
Structure of human holocarboxylase synthetase gene and mutation spectrum of holocarboxylase synthetase deficiency 总被引:4,自引:0,他引:4
Xue Yang Yoko Aoki Xue Li Osamu Sakamoto Masahiro Hiratsuka Shigeo Kure Sepidh Taheri Ernst Christensen Koji Inui Mitsuru Kubota Miki Ohira Misao Ohki Jun Kudoh Kazuhiko Kawasaki Kazunori Shibuya Ai Shintani Shuichi Asakawa Shinsei Minoshima Nobuyoshi Shimizu Kuniaki Narisawa Yoichi Matsubara Yoichi Suzuki 《Human genetics》2001,109(5):526-534
Holocarboxylase synthetase (HLCS) is an enzyme that catalyzes the incorporation of biotin into apo-carboxylases, and its deficiency causes biotin-responsive multiple carboxylase deficiency. The reported sequences of cDNA for human HLCS from liver, lymphocyte, and KG-1 myeloid cell lines differ at their 5' regions. To elucidate variations of the human HLCS mRNA and longer 5' cDNA ends, we performed screening of the human liver cDNA library and rapid amplification of the cDNA ends (RACE). Our results suggest the existence of three types of HLCS mRNA that start at different exons. The first type starts at exon 1, and the second type starts at exon 3, and both are found in various human tissues. The third type, corresponding to the cDNA from the KG-1 cell, starts at exon 2 of the HLCS gene. Various splicing patterns from exons 3-6 were also observed. None of the variations of cDNA found created a new initiation codon. Mutation screening from exons 6-14, therefore, was sufficient to detect amino acid changes in HLCS in patients. Our direct sequencing strategy for screening mutations in the HLCS gene revealed mutations in five Japanese patients and seven non-Japanese patients. Our analyses involving 12 Japanese and 13 non-Japanese patients and studies by others indicate that (1) there is no panethnically prevalent mutation; (2) the Arg508Trp, Gly581Ser, and Val550Met mutations are found in both Japanese and non-Japanese populations; (3) the IVS10+5G-->A mutation is predominant and probably a founder mutation in European patients; (4) the 655-656insA, Leu237Pro, and 780delG mutations are unique in Japanese patients; (5) the spectrum of the mutations in the HLCS gene may vary substantially among different ethnic groups. 相似文献
998.
999.
Yoshida M Mori A Morimoto S Kotani E Oka M Notoya K Makino H Ono M Shirasaki M Tada N Fujita H Ban J Ikeda Y Kawamoto T Goto M Kimura H Baba A Yasuma T 《Bioorganic & medicinal chemistry》2011,19(6):1881-1894
The calcium-sensing receptor antagonist (CaSR) has been recognized as a promising target of anabolic agents for treating osteoporosis. In the course of developing a new drug candidate for osteoporosis, we found tetrahydropyrazolopyrimidine derivative 1 to be an orally active CaSR antagonist that stimulated transient PTH secretion in rats. However, compound 1 showed poor physical and chemical stability. In order to work out this compound's chemical stability and further understand its in vivo efficacy, we focused on modifying the 2-position of the tetrahydropyrazolopyrimidine. As a result of chemical modification, we discovered (5R)-N-[1-ethyl-1-(4-ethylphenyl)propyl]-2,7,7-trimethyl-5-phenyl-4,5,6,7-tetrahydropyrazolo[1,5-a]pyrimidine-3-carboxamide monotosylate 10m (TAK-075), which showed improved solubility, chemical stability, and in vivo efficacy. Furthermore, we describe that evaluating the active metabolite is important during repeated treatment with short-acting CaSR antagonists. 相似文献
1000.
Marie Morgan-Fisher John R. Couchman Atsuko Yoneda 《The Journal of biological chemistry》2013,288(43):31229-31240
The Rho-associated protein kinases (ROCK I and II) are central regulators of important cellular processes such as migration and invasion downstream of the GTP-Rho. Recently, we reported collapsin response mediator protein (CRMP)-2 as an endogenous ROCK II inhibitor. To reveal how the CRMP-2-ROCK II interaction is controlled, we further mapped the ROCK II interaction site of CRMP-2 and examined whether phosphorylation states of CRMP-2 affected the interaction. Here, we show that an N-terminal fragment of the long CRMP-2 splice variant (CRMP-2L) alone binds ROCK II and inhibits colon carcinoma cell migration and invasion. Furthermore, the interaction of CRMP-2 and ROCK II is partially regulated by glycogen synthase kinase (GSK)-3 phosphorylation of CRMP-2, downstream of PI3K. Inhibition of PI3K reduced interaction of CRMP-2 with ROCK II, an effect rescued by simultaneous inhibition of GSK3. Inhibition of PI3K also reduced colocalization of ROCK II and CRMP-2 at the cell periphery in human breast carcinoma cells. Mimicking GSK3 phosphorylation of CRMP-2 significantly reduced CRMP-2 binding of recombinant full-length and catalytic domain of ROCK II. These data implicate GSK3 in the regulation of ROCK II-CRMP-2 interactions. Using phosphorylation-mimetic and -resistant CRMP-2L constructs, it was revealed that phosphorylation of CRMP-2L negatively regulates its inhibitory function in ROCK-dependent haptotactic cell migration, as well as invasion of human colon carcinoma cells. Collectively, the presented data show that CRMP-2-dependent regulation of ROCK II activity is mediated through interaction of the CRMP-2L N terminus with the ROCK II catalytic domain as well as by GSK3-dependent phosphorylation of CRMP-2. 相似文献