全文获取类型
收费全文 | 10509篇 |
免费 | 680篇 |
国内免费 | 1篇 |
专业分类
11190篇 |
出版年
2023年 | 65篇 |
2022年 | 129篇 |
2021年 | 219篇 |
2020年 | 147篇 |
2019年 | 180篇 |
2018年 | 261篇 |
2017年 | 204篇 |
2016年 | 324篇 |
2015年 | 533篇 |
2014年 | 508篇 |
2013年 | 776篇 |
2012年 | 853篇 |
2011年 | 784篇 |
2010年 | 539篇 |
2009年 | 469篇 |
2008年 | 608篇 |
2007年 | 586篇 |
2006年 | 587篇 |
2005年 | 521篇 |
2004年 | 494篇 |
2003年 | 461篇 |
2002年 | 438篇 |
2001年 | 80篇 |
2000年 | 70篇 |
1999年 | 80篇 |
1998年 | 108篇 |
1997年 | 100篇 |
1996年 | 65篇 |
1995年 | 87篇 |
1994年 | 73篇 |
1993年 | 63篇 |
1992年 | 48篇 |
1991年 | 56篇 |
1990年 | 49篇 |
1989年 | 39篇 |
1988年 | 40篇 |
1987年 | 31篇 |
1986年 | 18篇 |
1985年 | 38篇 |
1984年 | 57篇 |
1983年 | 41篇 |
1982年 | 35篇 |
1981年 | 49篇 |
1980年 | 32篇 |
1979年 | 26篇 |
1978年 | 28篇 |
1977年 | 22篇 |
1976年 | 20篇 |
1975年 | 25篇 |
1974年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
Knowiedge on community structure of North Sea meiofauna has greatly increased recently. A quasisynoptic picture of meiofauna
densities and copepod community structure from 171 stations of the southern North Sea, sampled in April–May 1986, has been
obtained during the North Sea Benthos Survey. Latitudinal patterns in meiofauna abundance and copepod weight, abundance and
diversity exist in an area between 51°30′N and 58°30′N. Using TWINSPAN-classification five major groups of copepod species
can be recognized which are related to sediment type, latitude and depth. The part of the meiofauna in total benthic energy
flow, their role in the benthic food web and in biogeochemical cycles is discussed based on existing literature. There are
still considerable gaps in knowledge and the field is not progressing rapidly.
Publication no. 599 Netherlands Institute of Ecology, Centre for Estuarine and Coastal Ecology, Yerseke, The Netherlands. 相似文献
22.
Angelo F. Borghetti Mariarosaria Tramacere Paolo Ghiringhelli Alberto Severini John E. Kay 《生物化学与生物物理学报:生物膜》1981,646(2):218-230
Changes in neutral amino acid transport activity caused by addition of phytohaemagglutinin-P to quiescent peripheral pig lymphocytes have been evaluated by measurements of 14C-labelled neutral and analogue amino acids under conditions approaching initial entry rates. Utilizing methylaminoisobutyric acid, the best model substrate of System A, we confirmed our previous report (Borghetti, A.F., Kay, J.E. and Wheeler, K.P. (1979) Biochem. J. 182, 27–32) on the absence of this transport system in quiescent cells and its emergence following stimulation. Furthermore, we demonstrated the presence in quiescent cells of an Na+-dependent transport system for neutral amino acids that has been characterized as System ASC by several criteria including intolerance to methylaminoisobutyric acid, strict Na+-dependence, the property of transtimulation and specificity for pertinent substrates such as alanine, serine, cysteine and threonine. Analysis of the relationship between influx and substrate concentration revealed that two independent saturable components contribute to entry of alanine in quiescent cells: a low affinity () and a high affinity () component. The high affinity component could be inhibited in a competitive way by serine, cysteine and threonine, but methylaminoisobutyric acid did not change appreciably its constants. The enhanced activity of alanine transport through the ASC system observed in activated cells resulted from a large increase in the capacity () of the high affinity component without any substantial change in the apparent affinity constant (). 相似文献
23.
24.
Umberto Tomati Giovanni Giovannozzi-Sermanni Silvestro Duprè Carlo Cannella 《Phytochemistry》1976,15(5):597-598
The NADH: nitrate reductase from durum wheat leaves was inactivated by cyanide and its activity restored by thiosulphate and beef kidney rhodanese. Rhodanese and thiosulphate, added to NADH-nitrate reductase before cyanide treatment protected NADH-nitrate reductase activity. No oxidizing agent was required for the protection or restoration of cyanide treated NADH-nitrate reductase. 相似文献
25.
26.
Neus Mestre-Farrs Santiago Guerrero Nadine Bley Ezequiel Rivero Olga Coll Eva Borrs Eduard Sabid Alberto Indacochea Carlos Casillas-Serra Aino
I Jrvelin Baldomero Oliva Alfredo Castello Stefan Hüttelmaier Ftima Gebauer 《Nucleic acids research》2022,50(14):8207
RNA-binding proteins (RBPs) have been relatively overlooked in cancer research despite their contribution to virtually every cancer hallmark. Here, we use RNA interactome capture (RIC) to characterize the melanoma RBPome and uncover novel RBPs involved in melanoma progression. Comparison of RIC profiles of a non-tumoral versus a metastatic cell line revealed prevalent changes in RNA-binding capacities that were not associated with changes in RBP levels. Extensive functional validation of a selected group of 24 RBPs using five different in vitro assays unveiled unanticipated roles of RBPs in melanoma malignancy. As proof-of-principle we focused on PDIA6, an ER-lumen chaperone that displayed a novel RNA-binding activity. We show that PDIA6 is involved in metastatic progression, map its RNA-binding domain, and find that RNA binding is required for PDIA6 tumorigenic properties. These results exemplify how RIC technologies can be harnessed to uncover novel vulnerabilities of cancer cells. 相似文献
27.
Hoogsteen (HG) base pairing is characterized by a 180° rotation of the purine base with respect to the Watson-Crick-Franklin (WCF) motif. Recently, it has been found that both conformations coexist in a dynamical equilibrium and that several biological functions require HG pairs. This relevance has motivated experimental and computational investigations of the base-pairing transition. However, a systematic simulation of sequence variations has remained out of reach. Here, we employ advanced path-based methods to perform unprecedented free-energy calculations. Our methodology enables us to study the different mechanisms of purine rotation, either remaining inside or after flipping outside of the double helix. We study seven different sequences, which are neighbor variations of a well-studied A⋅T pair in A6-DNA. We observe the known effect of A⋅T steps favoring HG stability, and find evidence of triple-hydrogen-bonded neighbors hindering the inside transition. More importantly, we identify a dominant factor: the direction of the A rotation, with the 6-ring pointing either towards the longer or shorter segment of the chain, respectively relating to a lower or higher barrier. This highlights the role of DNA’s relative flexibility as a modulator of the WCF/HG dynamic equilibrium. Additionally, we provide a robust methodology for future HG proclivity studies. 相似文献
28.
29.
Angiogenesis is a fundamental step in several important physiological events and pathological conditions including embryonic development, wound repair, tumor growth and metastasis. PRKX was identified as a novel type-I cAMP-dependent protein kinase gene expressed in multiple developing tissues. PRKX has also been shown to be phylogenetically and functionally distinct from PKA. This study presents the first evidence that PRKX stimulates endothelial cell proliferation, migration, and vascular-like structure formation, which are the three essential processes for angiogenesis. In contrast, classic PKA demonstrated an inhibitory effect on endothelia vascular-like structure formation. Our findings suggest that PRKX is an important protein kinase engaged in the regulation of angiogenesis and could play critical roles in various physiological and pathological conditions involving angiogenesis. PRKX binds to Pin-1, Magi-1 and Bag-3, which regulate cell proliferation, apoptosis, differentiation and tumorigenesis. The interaction of PRKX with Pin-1, Magi-1 and Bag-3 could contribute to the stimulating role of PRKX in angiogenesis. 相似文献
30.