全文获取类型
收费全文 | 11835篇 |
免费 | 915篇 |
国内免费 | 3篇 |
专业分类
12753篇 |
出版年
2023年 | 77篇 |
2022年 | 99篇 |
2021年 | 180篇 |
2020年 | 170篇 |
2019年 | 144篇 |
2018年 | 337篇 |
2017年 | 301篇 |
2016年 | 384篇 |
2015年 | 568篇 |
2014年 | 593篇 |
2013年 | 760篇 |
2012年 | 1039篇 |
2011年 | 1035篇 |
2010年 | 607篇 |
2009年 | 490篇 |
2008年 | 834篇 |
2007年 | 762篇 |
2006年 | 701篇 |
2005年 | 669篇 |
2004年 | 637篇 |
2003年 | 533篇 |
2002年 | 473篇 |
2001年 | 152篇 |
2000年 | 131篇 |
1999年 | 102篇 |
1998年 | 76篇 |
1997年 | 66篇 |
1996年 | 69篇 |
1995年 | 59篇 |
1994年 | 40篇 |
1993年 | 55篇 |
1992年 | 53篇 |
1991年 | 34篇 |
1990年 | 43篇 |
1989年 | 28篇 |
1988年 | 20篇 |
1987年 | 26篇 |
1986年 | 27篇 |
1985年 | 32篇 |
1984年 | 25篇 |
1983年 | 31篇 |
1982年 | 30篇 |
1981年 | 19篇 |
1980年 | 17篇 |
1979年 | 28篇 |
1978年 | 30篇 |
1977年 | 15篇 |
1976年 | 22篇 |
1975年 | 24篇 |
1973年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
931.
Phloea subquadrata Spinola, 1837 (Pentatomoidea: Phloeidae) belongs to a small family of sap feeding bugs that live on tree trunks, on which they are cryptic because of their coloration and flat body. There are a few studies concerning phloeid anatomy and biology, but almost nothing is known about their ecology. In this study, population dynamics and structure of P. subquadrata on the host tree Plinia cauliflora (Myrtaceae) were investigated during 3 yr in a semideciduous forest in southeast Brazil. Nymphs and adults were active all year round, but the egg-laying season was mainly restricted to the warm, rainy season (September-March). Population density slightly increased at the end of this season because of reproduction. Population age structure changed markedly over time, with nymphs reaching the adult stage in the subsequent early-to-mid rainy season. Abiotic factors, such as rainfall and temperature, were correlated with female oviposition and population dynamics and phenology. Sex ratio was male-biased, not differing from 1:1 only during the adult recruitment period (October-January). Under dry weather conditions, phloeids were distributed closer to the base of the tree trunks when compared with rainy conditions. Our results suggest that seasonality and variations in weather conditions are important driving forces of population dynamics and phenology of P. subquadrata, as well as the microhabitat selection on host trees. 相似文献
932.
Charles Van der Henst Caroline Charlier Michaël Deghelt Johan Wouters Jean-Yves Matroule Jean-Jacques Letesson Xavier De Bolle 《BMC microbiology》2010,10(1):248
Background
When heterologous recombinant proteins are produced in Escherichia coli, they often precipitate to form insoluble aggregates of unfolded polypeptides called inclusion bodies. These structures are associated with chaperones like IbpA. However, there are reported cases of "non-classical" inclusion bodies in which proteins are soluble, folded and active. 相似文献933.
934.
Assessing estuarine quality under the ecosystem services scope: Ecological and socioeconomic aspects
Rute Pinto Joana Patrício João Magalhães Neto Fuensanta Salas João Carlos Marques 《Ecological Complexity》2010,7(3):389-402
An increasing need for integrative assessments that measure the contributions of the environment to human welfare has recently been recognised. In the present study, a preliminary assessment of the services provided by the Mondego Basin in terms of system ecological quality was carried out. The ecological, economic, and societal relations of the Mondego estuarine services were analysed. An inventory of the main ecosystem services provided by the Mondego system was performed. The conditions and trends of the main services (food production, recreation and water quality maintenance) were determined, and the scale dependence of this assessment was interpolated on three different scales: Mondego Basin, Lower Mondego, and Mondego Estuary. The interdependence among services was quantified; an ecological assessment regarding water quality and ecological conditions was performed, and a preliminary valuation of the food production, recreation and tourism in the region was undertaken. In the study system, from 1992 to 2006, there was an increase in recreation activities and water uses and a simultaneous decrease in services such as food production (i.e., strong interdependence among services). Ecological quality improvement is reflected in both local communities’ diversity and water quality. The market prices method was used to estimate the values for the three services considered; however, the Mondego catchment's full value cannot be calculated without estimating the real wetlands value because these are prone to underestimation. Uncertainties and shortcomings regarding the reliability of this kind of assessment for implementation on estuarine ecosystems are discussed. 相似文献
935.
Delphine Benaitreau Esther Dos Santos Marie-Christine Leneveu Philippe De Mazancourt René Pecquery Marie-Noëlle Dieudonné 《Reproductive biology and endocrinology : RB&E》2010,8(1):128
Background
In human pregnancy, a correct placentation depends on trophoblast proliferation, differentiation, migration and invasion. These processes are highly regulated by placental hormones, growth factors and cytokines. Recently, we have shown that adiponectin, an adipokine, has anti-proliferative effects on trophoblastic cells. Here, we complete this study by demonstrating that adiponectin modulates BeWo and human villous cytotrophoblast cell differentiation. 相似文献936.
Marijn Rutgers Daniël BF Saris Wouter JA Dhert Laura B Creemers 《Arthritis research & therapy》2010,12(3):R114
Introduction
Intraarticular administration of autologous conditioned serum (ACS) recently demonstrated some clinical effectiveness in treatment of osteoarthritis (OA). The current study aims to evaluate the in vitro effects of ACS on cartilage proteoglycan (PG) metabolism, its composition and the effects on synovial fluid (SF) cytokine levels following intraarticular ACS administration. 相似文献937.
Justin H Fransen Johan van der Vlag Jurjen Ruben Gosse J Adema Jo H Berden Luuk B Hilbrands 《Arthritis research & therapy》2010,12(2):207
The etiology of the autoimmune disease systemic lupus erythematosus is not known, but aberrant apoptosis and/or insufficient
clearance of apoptotic material have been assigned a pivotal role. During apoptosis, nucleosomes and several endogenous danger-associated
molecular patterns are incorporated in blebs. Recent data indicate that apoptotic blebs induce maturation of myeloid dendritic
cells, resulting in IL-17 production by T cells. In this review we summarize current knowledge on the role of dendritic cells
in the pathogenesis of systemic lupus erythematosus with special emphasis on the uptake of apoptotic blebs by dendritic cells,
and the subsequent induction of Th17 cells. 相似文献
938.
Piret G Desmet R Diesis E Drobecq H Segers J Rouanet C Debrie AS Boukherroub R Locht C Melnyk O 《Journal of proteome research》2010,9(12):6467-6478
Peptide microarrays are useful tools for the characterization of humoral responses against peptide antigens. The study of post-translational modifications requires the printing of appropriately modified peptides, whose synthesis can be time-consuming and expensive. We describe here a method named "chips from chips", which allows probing the presence of antibodies directed toward modified peptide antigens starting from unmodified peptide microarrays. The chip from chip concept is based on the modification of peptide microspots by simple chemical reactions. The starting peptide chip (parent chip) is covered by the reagent solution, thereby allowing the modification of specific residues to occur, resulting in the production of a modified peptide chip (daughter chip). Both parent and daughter chips can then be used for interaction studies. The method is illustrated using reductive methylation for converting lysines into dimethyllysines. The rate of methylation was studied using specific antibodies and fluorescence detection, or surface-assisted laser desorption ionization mass spectrometry. This later technique showed unambiguously the efficient methylation of the peptide probes. The method was then used to study the humoral response against the Mycobacterium tuberculosis heparin-binding hemagglutinin, a methylated surface-associated virulence factor and powerful diagnostic and protective antigen. 相似文献
939.
940.