全文获取类型
收费全文 | 2717篇 |
免费 | 141篇 |
专业分类
2858篇 |
出版年
2023年 | 7篇 |
2022年 | 27篇 |
2021年 | 47篇 |
2020年 | 23篇 |
2019年 | 33篇 |
2018年 | 57篇 |
2017年 | 28篇 |
2016年 | 67篇 |
2015年 | 103篇 |
2014年 | 109篇 |
2013年 | 140篇 |
2012年 | 200篇 |
2011年 | 198篇 |
2010年 | 133篇 |
2009年 | 101篇 |
2008年 | 178篇 |
2007年 | 174篇 |
2006年 | 169篇 |
2005年 | 139篇 |
2004年 | 197篇 |
2003年 | 173篇 |
2002年 | 124篇 |
2001年 | 32篇 |
2000年 | 31篇 |
1999年 | 30篇 |
1998年 | 21篇 |
1997年 | 17篇 |
1996年 | 20篇 |
1995年 | 19篇 |
1994年 | 18篇 |
1993年 | 17篇 |
1992年 | 18篇 |
1991年 | 27篇 |
1990年 | 24篇 |
1989年 | 18篇 |
1988年 | 14篇 |
1987年 | 14篇 |
1986年 | 14篇 |
1985年 | 9篇 |
1984年 | 12篇 |
1983年 | 14篇 |
1982年 | 12篇 |
1981年 | 9篇 |
1978年 | 7篇 |
1977年 | 7篇 |
1975年 | 6篇 |
1974年 | 3篇 |
1969年 | 2篇 |
1968年 | 2篇 |
1967年 | 2篇 |
排序方式: 共有2858条查询结果,搜索用时 15 毫秒
101.
A capsule containing an aromatase inhibitor (4-androsten-4-ol-3,17-dione) was subcutaneously implanted in four oligozoospermic beagle dogs and one azoospermic beagle dog with high plasma estradiol-17beta (E2) concentrations (15-19 pg/ml) and low plasma testosterone (T) concentrations (0.6-0.8 ng/ml) for 8 weeks and the effect of the aromatase inhibitor on spermatogenic dysfunction was assessed. Plasma E2 and T concentrations and semen quality were examined at 1 week intervals from 3 weeks before to 12 weeks after the start of treatment. Testicular biopsies were done twice (capsule implantation and removal). Plasma E2 concentrations of all dogs decreased (9-14 pg/ml) and plasma T concentrations increased (2.0-2.6 ng/ml) from 3 weeks after capsule implantation to capsule removal. The mean number of spermatozoa ejaculated by all four oligozoospermic dogs between 4 and 9 weeks after implantation was higher (127 x 10(6) to 205 x 10(6)) than before implantation (20 x 10(6) to 38 x 10(6)) (P < 0.05 and 0.01). Very low numbers (2 x 10(4) to 4 x 10(4)) of immotile spermatozoa were observed between 7 and 8 weeks after implantation in the semen collected from the dog with azoospermia. Before implantation, a few spermatozoa were seen in only one-fifth of the seminiferous tubules in this dog; 8 weeks after implantation, the mean diameter and mean number of round spermatids in the seminiferous tubules in all five dogs were higher than before implantation (P < 0.05). Implantation of the capsule containing the aromatase inhibitor in infertile dogs with abnormally high plasma E2 concentrations improved their spermatogenic function, concurrent with decreased plasma E2 and increased plasma T. 相似文献
102.
Ryo Nagao Akira Moriguchi Tatsuya Tomo Ayako Niikura Saori Nakajima Takehiro Suzuki Akinori Okumura Masako Iwai Jian-Ren Shen Masahiko Ikeuchi Isao Enami 《The Journal of biological chemistry》2010,285(38):29191-29199
Oxygen-evolving photosystem II (PSII) isolated from a marine centric diatom, Chaetoceros gracilis, contains a novel extrinsic protein (Psb31) in addition to four red algal type extrinsic proteins of PsbO, PsbQ′, PsbV, and PsbU. In this study, the five extrinsic proteins were purified from alkaline Tris extracts of the diatom PSII by anion and cation exchange chromatographic columns at different pH values. Reconstitution experiments in various combinations with the purified extrinsic proteins showed that PsbO, PsbQ′, and Psb31 rebound directly to PSII in the absence of other extrinsic proteins, indicating that these extrinsic proteins have their own binding sites in PSII intrinsic proteins. On the other hand, PsbV and PsbU scarcely rebound to PSII alone, and their effective bindings required the presence of all of the other extrinsic proteins. Interestingly, PSII reconstituted with Psb31 alone considerably restored the oxygen evolving activity in the absence of PsbO, indicating that Psb31 serves as a substitute in part for PsbO in supporting oxygen evolution. A significant difference found between PSIIs reconstituted with Psb31 and with PsbO is that the oxygen evolving activity of the former is scarcely stimulated by Cl− and Ca2+ ions but that of the latter is largely stimulated by these ions, although rebinding of PsbV and PsbU activated oxygen evolution in the absence of Cl− and Ca2+ ions in both the former and latter PSIIs. Based on these results, we proposed a model for the association of the five extrinsic proteins with intrinsic proteins in diatom PSII and compared it with those in PSIIs from the other organisms. 相似文献
103.
Tatsuya Kawamoto Yoshifumi Kobayashi Hidenori Nakajima Yukiko Yamagishi 《Biochemical and biophysical research communications》2013
Vascular network formation is a key therapeutic event in regenerative medicine because it is essential for mitigating or ameliorating ischemic conditions implicated in various diseases and repair of tissues and organs. In this study, we induced human induced pluripotent stem cells (hiPSCs) to differentiate into heterogeneous cell populations which have abilities to form vascular vessel-like structures by recapitulating the embryonic process of vasculogenesis in vitro. These cell populations, named cardiovascular blast populations (CBPs) in this report, primarily consisted of CD31+ and CD90+ cells. 相似文献
104.
105.
Keiichi Konoki Tatsuya Onoda Sachie Furumochi Yuko Cho Mari Yotsu-Yamashita Takeshi Yasumoto 《Bioorganic & medicinal chemistry letters》2013,23(21):5833-5835
The binding between [24-3H]okadaic acid (OA) and a recombinant OA binding protein OABP2.1 was examined using various OA analog, including methyl okadaate, norokadanone, 7-deoxy OA, and 14,15-dihydro OA, 7-O-palmitoyl DTX1, to investigate the structure activity relationship. Among them, 7-O-palmitoyl DTX1, which is one of the diarrhetic shellfish poisoning (DSP) toxins identified in shellfish, displayed an IC50 for [24-3H]OA binding at 51 ± 6.3 nM (Mean ± SD). In addition, a synthetic compound, N-pyrenylmethyl okadamide, exhibited its IC50 at 10 ± 2.9 nM (Mean ± SD). These results suggested that the recombinant OABP2.1 and the N-pyrenylmethyl okadamide might be core substances in a novel assay for the DSP toxins. 相似文献
106.
Shin-ichi Makino Tatsuya Sawasaki Yaeta Endo Kazuyuki Takai 《Biochemical and biophysical research communications》2010,397(4):762-1054
Wheat RNA ligase contains 5′-hydroxyl kinase, 2′,3′-cyclic phosphate 3′-phosphodiesterase, and 5′-phosphate 2′-phosphate-3′-hydroxyl RNA ligase activities in a 110-kDa polypeptide. Taking advantage of a wheat cell-free protein production system, we prepared various fragments containing a part of the enzyme. The method allowed us to check the activities of the fragments rapidly, eliminating the time-consuming cloning and sequencing steps for the expression of the fragment proteins. The results showed that each of the three activities can be assigned to a non-overlapping domain that does not require the presence of the other part(s) of the enzyme for its activity. This contrasts to the case of yeast tRNA ligase, in which the central kinase domain has been suggested to require to be tethered to one of the flanking domains for its activity. 相似文献
107.
Nojima T Murayama S Yoshida M Motojima F 《The Journal of biological chemistry》2008,283(26):18385-18392
A double-heptamer ring chaperonin GroEL binds denatured substrate protein, ATP, and GroES to the same heptamer ring and encapsulates substrate into the central cavity underneath GroES where productive folding occurs. GroES is a disk-shaped heptamer, and each subunit has a GroEL-binding loop. The residues of the GroEL subunit responsible for GroES binding largely overlap those involved in substrate binding, and the mechanism by which GroES can replace the substrate when GroES binds to GroEL/substrate complex remains to be clarified. To address this question, we generated single polypeptide GroES by fusing seven subunits with various combinations of active and GroEL binding-defective subunits. Functional tests of the fused GroES variants indicated that four active GroES subunits were required for efficient formation of the stable GroEL/GroES complex and five subunits were required for the productive GroEL/substrate/GroES complex. An increase in the number of defective GroES subunits resulted in a slowing of encapsulation and folding. These results indicate the presence of an intermediate GroEL/substrate/GroES complex in which the substrate and GroES bind to GroEL by sharing seven common binding sites. 相似文献
108.
109.
Yamano K Unuma T 《Comparative biochemistry and physiology. Part A, Molecular & integrative physiology》2006,143(2):155-161
We analyzed the expressed sequence tags (ESTs) obtained from a cDNA library of the eyestalk of the kuruma prawn, Marsupenaeus japonicus, to examine gene expression profile with special focus on female reproduction. The assembly of 1988 ESTs created 136 contigs from 738 ESTs; however 1250 ESTs remained singletons. Significant similarities (blast score > or = 50 bits) to the DNA sequences in the databank were found for only 16.7% of the 1386 sequences (136 contigs plus 1250 singletons), suggesting that the eyestalk library contains many unknown genes. Ribosomal RNA and mitochondrial respiration enzymes with significant similarities were found abundantly in the ESTs, whereas genes related to maturation or endocrine systems were scarce. Three ESTs were assumed to encode novel eyestalk hormones with marked similarities to pigment-dispersing hormone, molt-inhibiting hormone and crustacean hyperglycemic hormone. Sequences encoding a product highly homologous to farnesoic acid O-methyltransferase, an enzyme that produces methyl farnesoate, were also found. 相似文献
110.
Mitani Y Sato K Muramoto Y Karakawa T Kitamado M Iwanaga T Nabeshima T Maruyama K Nakagawa K Ishida K Sasamoto K 《Biochemical and biophysical research communications》2008,372(1):19-23
Pirfenidone (PFD) is focused on a new anti-fibrotic drug, which can minimize lung fibrosis etc. We evaluated the superoxide () scavenging activities of PFD and the PFD-iron complex by electron spin resonance (ESR) spectroscopy, luminol-dependent chemiluminescence assay, and cytochrome c reduction assay. Firstly, we confirmed that the PFD-iron complex was formed by mixing iron chloride with threefold molar PFD, and the complex was stable in distillated water and ethanol. Secondary, the PFD-iron complex reduced the amount of produced by xanthine oxidase/hypoxanthine without inhibiting the enzyme activity. Thirdly, it also reduced the amount of released from phorbor ester-stimulated human neutrophils. PFD alone showed few such effects. These results suggest the possibility that the scavenging effect of the PFD-iron complex contributes to the anti-fibrotic action of PFD used for treating idiopathic pulmonary fibrosis. 相似文献