全文获取类型
收费全文 | 99971篇 |
免费 | 833篇 |
国内免费 | 880篇 |
专业分类
101684篇 |
出版年
2023年 | 57篇 |
2022年 | 108篇 |
2021年 | 222篇 |
2020年 | 141篇 |
2019年 | 154篇 |
2018年 | 11969篇 |
2017年 | 10779篇 |
2016年 | 7678篇 |
2015年 | 999篇 |
2014年 | 712篇 |
2013年 | 807篇 |
2012年 | 4854篇 |
2011年 | 13400篇 |
2010年 | 12337篇 |
2009年 | 8555篇 |
2008年 | 10237篇 |
2007年 | 11734篇 |
2006年 | 657篇 |
2005年 | 845篇 |
2004年 | 1261篇 |
2003年 | 1254篇 |
2002年 | 1030篇 |
2001年 | 300篇 |
2000年 | 199篇 |
1999年 | 73篇 |
1998年 | 50篇 |
1997年 | 57篇 |
1996年 | 41篇 |
1995年 | 34篇 |
1994年 | 34篇 |
1993年 | 46篇 |
1992年 | 59篇 |
1991年 | 66篇 |
1990年 | 28篇 |
1989年 | 34篇 |
1988年 | 31篇 |
1987年 | 31篇 |
1986年 | 21篇 |
1985年 | 19篇 |
1984年 | 17篇 |
1983年 | 27篇 |
1982年 | 14篇 |
1980年 | 16篇 |
1977年 | 12篇 |
1975年 | 12篇 |
1972年 | 252篇 |
1971年 | 278篇 |
1965年 | 14篇 |
1962年 | 24篇 |
1944年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Wen Wang Yan Zhao Shujuan Yao Xiujuan Cui Wenying Pan Wenqian Huang Jiangang Gao Taotao Dong Shiqian Zhang 《Biochemistry. Biokhimii?a》2017,82(8):933-941
Epithelial ovarian cancer (EOC) has the highest mortality among various types of gynecological malignancies. Most patients die of metastasis and recurrence due to cisplatin resistance. Thus, it is urgent to develop novel therapies to cure this disease. CCK-8 assay showed that nigericin exhibited strong cytotoxicity on A2780 and SKOV3 cell lines. Flow cytometry indicated that nigericin could induce cell cycle arrest at G0/G1 phase and promote cell apoptosis. Boyden chamber assay revealed that nigericin could inhibit migration and invasion in a dose-dependent manner by suppressing epithelial–mesenchymal transition (EMT) in EOC cells. These effects were mediated, at least partly, by the Wnt/β-catenin signaling pathway. Our results demonstrated that nigericin could inhibit EMT during cell invasion and metastasis through the canonical Wnt/β-catenin signaling pathway. Nigericin may prove to be a novel therapeutic strategy that is effective in patients with metastatic EOC. 相似文献
992.
Telomerase expression strongly correlates with the grade of malignancy in glioma with inhibition illustrating a definite increase
in chemosensitivity. This study was designed to investigate the effects of a green tea derivative, epigallocatechin-3-gallate
(EGCG); together with either cisplatin or tamoxifen in glioma, and to investigate whether these effects are mediated through
telomerase suppression. EGCG showed a significant cytotoxic effect on 1321N1 cells after 24 h and on U87-MG cells after 72 h
(P < 0.001) without significantly affecting the normal astrocytes. Treatment with EGCG inhibited telomerase expression significantly
(P < 0.01) and enhanced the effect of cisplatin and tamoxifen in both 1321N1 (P < 0.01) and U87-MG (P < 0.001) cells. EGCG, as a natural product has enormous potential to be an anti-cancer agent capable of enhancing tumour
cell sensitivity to therapy. 相似文献
993.
In studying plant colonization by inoculated Fusarium oxysporum endophytes, it is important to be able to distinguish inoculated isolates from saprophytic strains. In the current study, F. oxysporum isolates were transformed with the green (GFP) and red fluorescent protein (DsRed) genes, and benomyl- and chlorate-resistant mutant isolates were also developed. The benomyl- and chlorate-resistant mutants, and the fluorescently labelled transformants, were able to grow on potato dextrose agar amended with 20 mg Benlate® l?1, 30 g chlorate l?1 and 150 μg hygromycin ml?1, respectively. Single spores of all mutants remained stable after several transfers on non-selective media. Most mutants and transformants produced colony diameters that did not differ significantly from that of their wild-type progenitors after 7 days of growth on non-selective media. Few mutants, however, had growth rates that were either slower or faster than for their wild-types. Plant colonization studies showed that root and rhizome tissue colonization by most benomyl- and chlorate-resistant mutants was similar to that of their wild-type isolates. Unlike GFP transformants, DsRed transformants were difficult to visualize in planta. Both the mutants and transformants can be used for future studies to investigate colonization, distribution and survival of biocontrol F. oxysporum endophytes in banana plants. 相似文献
994.
The biomass and productivity of Schima superba-Castanopsis carlesii forests in Tiantong, Zhejiang Province, were determined using overlapping quadrants and stem analyses. The total community
biomass was (225.3±30.1) t hm−2, of which the aboveground parts accounted for 72.0% and the underground parts accounted for 28.0%. About 87.2% of biomass
existed in the tree layer. The resprouting biomass was small, of which over 95.0% occurred in the shrub layer. The productivity
of the aboveground parts of the community was (386.8±98.9) g m−2a−1, in which more than 96.0% was present at the tree level. The trunk’s contribution to productivity was the greatest, while
that of leaves was the smallest. In China, the community biomass of subtropical evergreen broadleaved forests differs significantly
with the age of the forest. The community biomass of the 52-year-old S. superba-C. carlesii forests in this study was lower than the average biomass of subtropical evergreen broadleaved forests in China, and was lower
than the biomass of other subtropical evergreen broadleaved forests elsewhere in the world. Moreover, its productivity was
lower than the model estimate, indicating that without disturbance, this community has great developmental potential in terms
of community biomass and productivity. 相似文献
995.
Nakazawa Y Sagane Y Kikuchi T Uchino M Nagai T Sato H Toeda K Takano K 《The protein journal》2010,29(8):598-608
We previously isolated Streptomyces racemochromogenes strain 10-3, which produces a phospholipase D (PLD) with high transphosphatidylation activity. Here, we purified and cloned
the PLD (PLD103) from the strain. PLD103 exerted the highest hydrolytic activity at a slightly alkaline pH, which is in contrast
to the majority of known Streptomyces PLDs that have a slightly acidic optimum pH. PLD103 shares only 71–76% amino acid sequence identity with other Streptomyces PLDs that have a slightly acidic optimum pH; thus, the diversity in the primary structure might explain the discrepancy observed
in the optimum pH. The purified PLD displayed high transphosphatidylation activity in the presence of glycerol, l-serine, and 2-aminoethanol hydrochloride with a conversion rate of 82–97% in a simple one-phase system, which was comparable
to the rate of other Streptomyces PLDs in a complicated biphasic system. 相似文献
996.
Daniela Giordano Roberta Russo Daniela Coppola Giovanna Altomonte Guido di Prisco Stefano Bruno Cinzia Verde 《Hydrobiologia》2015,761(1):293-312
Notothenioidei, the taxonomic group of teleosts that dominates the Southern Ocean and dwell in the Ross Sea at large, provide an example of marine species that underwent unique adaptations to life at low temperatures and high oxygen concentrations, resulting in morphological, physiological, genomic, and biochemical peculiarities in comparison with warm-water fish. Global Warming raises concerns over the fate of these stenothermal fish, as their adaptation has been accompanied by irreversible genomic losses, which suggest a poor genetic potential to adapt to warmer climates. Specifically, this review focuses on adaptation of proteins belonging to the globin superfamily, which include the respiratory proteins hemoglobin and myoglobin and the non-respiratory proteins neuroglobin and cytoglobin. Here, we describe their molecular adaptations to cold temperatures in the framework of the physiology of oxygen transport and management of oxidative stress in fish species largely populating the Ross Sea. 相似文献
997.
The objectives of this work were to isolate the microorganisms responsible for a previously observed degradation of polycyclic
aromatic hydrocarbons (PAH) in soil and to test a method for cleaning a PAH-contaminated soil. An efficient PAH degrader was
isolated from an agricultural soil and designated as Mycobacterium LP1. In liquid culture, it degraded phenanthrene (58%), pyrene (24%), anthracene (21%) and benzo(a)pyrene (10%) present in mixture (initial concentration 50 μg ml−1 each) and phenanthrene (92%) and pyrene (94%) as sole carbon sources after 14 days of incubation at 30°C. In soil, Mycobacterium LP1 mineralised 14C-phenanthrene (45%) and 14C-pyrene (65%) after 10 days. The good ability of this Mycobacterium was combined with the benzo(a)pyrene oxidation effect obtained by 1% w/w rapeseed oil in a sequential treatment of a PAH-spiked soil (total PAH concentration
200 mg kg−1). The first step was incubation with the bacterium for 12 days and the second step was the addition of the rapeseed oil after
this time and a further incubation of 22 days. Phenanthrene (99%), pyrene (95%) and anthracene (99%) were mainly degraded
in the first 12 days and a total of 85% of benzo(a)pyrene was transformed during the whole process. The feasibility of the method is discussed. 相似文献
998.
Chabot N Vinatier V Gefflaut T Baudoin C Rodriguez F Blonski C Hoffmann P 《Journal of enzyme inhibition and medicinal chemistry》2008,23(1):21-27
The preparation of a phosphorylated alpha-dicarbonyl compound designed to specifically react with arginine residues of enzymes accepting phosphorylated compounds as effectors is reported, and shown to inhibit rabbit muscle aldolase in a time-dependent and irreversible manner. This irreversible inhibition occured in a buffer devoid of borate ions, suggesting that the presence of the phosphate moiety contributes in the stabilization of the adduct formed with arginine residues. Under the same conditions, the metalloenzyme iron superoxide dismutase, in which an arginine is known to be critical for the catalytic function, is not significantly inhibited. 相似文献
999.
Heterologous expression of genes involved in the biosynthesis of various products is of increasing interest in biotechnology and in drug research and development. Microbial cells are most appropriate for this purpose. Availability of more microbial genomic sequences in recent years has greatly facilitated the elucidation of metabolic and regulatory networks and helped gain overproduction of desired metabolites or create novel production of commercially important compounds. Saccharomyces cerevisiae, as one of the most intensely studied eukaryotic model organisms with a rich density of knowledge detailing its genetics, biochemistry, physiology, and large-scale fermentation performance, can be capitalized upon to enable a substantial increase in the industrial application of this yeast. In this review, we describe recent efforts made to produce commercial secondary metabolites in Saccharomyces cerevisiae as pharmaceuticals. As natural products are increasingly becoming the center of attention of the pharmaceutical and nutraceutical industries, such as naringenin, coumarate, artemisinin, taxol, amorphadiene and vitamin C, the use of S. cerevisiae for their production is only expected to expand in the future, further allowing the biosynthesis of novel molecular structures with unique properties. 相似文献
1000.
Lu Li Chettiyappan Visvanathan 《Reviews in Environmental Science and Biotechnology》2017,16(4):737-760
Following the rapid proliferation of organic pollutants in the surface water, the application of microfiltration technology has been extensively studied for its treatment since the 1990s. Given that the conventional treatment processes were unable to treat the excessive dissolved organic compounds, microfiltration technologies have gained momentum as effective solutions to treat the surface water. The efficacy of low-pressure membrane filtration technologies such as microfiltration and ultrafiltration has been under scrutiny ever since, and numerous research studies have aimed at enhancing their capabilities to reject the suspended solids and organic matters. This paper reviews the development trajectory of membrane technology, ranging from microfiltration to membrane bioreactors, for treating dissolved organic matters in surface water and their future potential. This is a critical review of the physicochemical and biological options such as, but not limited to, pretreatment of water using coagulation, ozonation, adsorption and/or a combination of these. On the whole, it is concluded that the membrane bioreactor system, which combines biological process and physical rejection, showed high potential in treating polluted surface water, which needs to be further investigated extensively to promote its application in water treatment plants. 相似文献