全文获取类型
收费全文 | 2490篇 |
免费 | 225篇 |
专业分类
2715篇 |
出版年
2022年 | 29篇 |
2021年 | 48篇 |
2020年 | 26篇 |
2019年 | 28篇 |
2018年 | 42篇 |
2017年 | 33篇 |
2016年 | 61篇 |
2015年 | 103篇 |
2014年 | 97篇 |
2013年 | 126篇 |
2012年 | 165篇 |
2011年 | 155篇 |
2010年 | 90篇 |
2009年 | 113篇 |
2008年 | 146篇 |
2007年 | 128篇 |
2006年 | 142篇 |
2005年 | 126篇 |
2004年 | 119篇 |
2003年 | 131篇 |
2002年 | 121篇 |
2001年 | 35篇 |
2000年 | 37篇 |
1999年 | 45篇 |
1998年 | 27篇 |
1997年 | 25篇 |
1996年 | 21篇 |
1995年 | 23篇 |
1994年 | 18篇 |
1993年 | 15篇 |
1992年 | 28篇 |
1991年 | 29篇 |
1990年 | 37篇 |
1989年 | 27篇 |
1988年 | 18篇 |
1987年 | 18篇 |
1986年 | 24篇 |
1985年 | 13篇 |
1984年 | 18篇 |
1983年 | 14篇 |
1982年 | 17篇 |
1981年 | 16篇 |
1980年 | 19篇 |
1979年 | 19篇 |
1978年 | 12篇 |
1976年 | 11篇 |
1973年 | 14篇 |
1972年 | 15篇 |
1971年 | 12篇 |
1970年 | 13篇 |
排序方式: 共有2715条查询结果,搜索用时 15 毫秒
101.
Dumont ER 《Integrative and comparative biology》2007,47(1):137-146
By any standard, bats are a successful group of mammals andthe evolution of flight and echolocation were certainly keyinnovations behind their success. That is only part of the story,however. Bats have diversified into trophic niches that rangefrom insectivory to feeding on blood, fruit, or nectar. Whileflight places fundamental constraints on the shape of the postcranialskeleton, skull shape in bats is remarkably diverse. Morphologicalstudies of individual families and sympatric assemblages demonstratethat variation in skull shape is clearly associated with trophicspecialization. Field experiments demonstrate that species-specificbiting behaviors during feeding are common and analyses indicatethat the evolution of cranial morphology and feeding behaviorare correlated. Modeling experiments further suggest that feeding(loading) behaviors and skull shape are functionally linked.If the skulls of bats are under selective pressure for minimalmass because of the energetic demands of flight, then they maybe more "optimized" to meet mechanical demands than are theskulls of other mammals. This would make bats a unique modelsystem for studying the evolution of diversity in skull shapeand its functional implications for the evolution of feedingstrategies in mammals. 相似文献
102.
Singh MK Dadke D Nicolas E Serebriiskii IG Apostolou S Canutescu A Egleston BL Golemis EA 《Molecular biology of the cell》2008,19(4):1627-1636
For over a decade, p130Cas/BCAR1, HEF1/NEDD9/Cas-L, and Efs/Sin have defined the Cas (Crk-associated substrate) scaffolding protein family. Cas proteins mediate integrin-dependent signals at focal adhesions, regulating cell invasion and survival; at least one family member, HEF1, regulates mitosis. We here report a previously undescribed novel branch of the Cas protein family, designated HEPL (for HEF1-Efs-p130Cas-like). The HEPL branch is evolutionarily conserved through jawed vertebrates, and HEPL is found in some species lacking other members of the Cas family. The human HEPL mRNA and protein are selectively expressed in specific primary tissues and cancer cell lines, and HEPL maintains Cas family function in localization to focal adhesions, as well as regulation of FAK activity, focal adhesion integrity, and cell spreading. It has recently been demonstrated that upregulation of HEF1 expression marks and induces metastasis, whereas high endogenous levels of p130Cas are associated with poor prognosis in breast cancer, emphasizing the clinical relevance of Cas proteins. Better understanding of the complete protein family should help inform prediction of cancer incidence and prognosis. 相似文献
103.
Estelle Dumont Véronique Fontaine Christophe Vuylsteker Hélène Sellier Sylvie Bodèle Najia Voedts Rosemonde Devaux Marlène Frise Komlan Avia Jean-Louis Hilbert Nasser Bahrman Eric Hanocq Isabelle Lejeune-Hénaut Bruno Delbreil 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》2009,118(8):1561-1571
To increase yield in pea (Pisum sativum L.), autumn sowing would be preferable. Hence, frost tolerance of pea became a major trait of interest for breeders. In order
to better understand the cold acclimation in pea, Champagne a frost tolerant line and Terese, a frost sensitive line, and
their recombinant inbred lines (RIL) were studied. RIL frost tolerance was evaluated by a frost damage scale under field as
well as controlled conditions. A quantitative trait loci (QTL) approach was used to identify chromosomal regions linked to
frost tolerance. The detected QTL explained from 6.5 to 46.5% of the phenotypic variance. Amongst them, those located on linkage
groups 5 and 6 were consistent with over all experiments, in field as well as in controlled environments. In order to improve
the understanding of the frost tolerance mechanisms, several cold acclimation key characters such as concentration of sugars,
electrolyte leakage, osmotic pressure, and activity of RuBisCO were assessed. Some of these physiological QTL colocalised
with QTL for frost damage, in particular two raffinose QTL on LG5 and LG6 and one RuBisCO activity QTL on LG6, explaining
8.8 to 27.0% of the phenotypic variance. In addition, protein quantitative loci were mapped; some of them colocalised with
frost damage and physiological QTL on LG5 and LG6, explaining 16.0–43.6% of the phenotypic variance. Raffinose metabolism
and RuBisCO activity and its effect on photosynthesis might play a major role in cold acclimation of pea.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
104.
S. Becquevort I. Dumont J.-L. Tison D. Lannuzel M.-L. Sauvée L. Chou V. Schoemann 《Polar Biology》2009,32(6):879-895
Pack ice, brines and seawaters were sampled in October 2003 in the East Antarctic sector to investigate the structure of the
microbial communities (algae, bacteria and protozoa) in relation to the associated physico-chemical conditions (ice structure,
temperature, salinity, inorganic nutrients, chlorophyll a and organic matter). Ice cover ranged between 0.3 and 0.8 m, composed of granular and columnar ice. The brine volume fractions
sharply increased above −4°C in the bottom ice, coinciding with an important increase of algal biomass (up to 3.9 mg C l−1), suggesting a control of the algae growth by the space availability at that period of time. Large accumulation of NH4
+ and PO4
3− was observed in the bottom ice. The high pool of organic matter, especially of transparent exopolymeric particles, likely
led to nutrients retention and limitation of the protozoa grazing pressure, inducing therefore an algal accumulation. In contrast,
the heterotrophs dominated in the underlying seawaters. 相似文献
105.
The production of prostaglandin E2 (PGE2) by cultured dog thyroid cells was high in a serum-containing medium and low in a serum-free, completely defined medium. Thyrotropin (TSH) and epidermal growth factor (EGF), two mitogenic factors for these cells, did not stimulate PGE2 release. Indomethacin, at a concentration which completely inhibited PGE2 production, had no effect on thyroid cell multiplication and DNA synthesis stimulated by TSH and EGF. It is concluded that cyclooxygenase products are not involved in the proliferation of canine thyroid cells and its control by TSH. 相似文献
106.
S Guibaud M Bonnet C Coicaud G Sournies A Combet J M Thoulon M Dumont 《Journal de génétique humaine》1980,28(1):61-62
From an observation, authors underline the interest of two complementary tests: ultrasonography and amniotic fluid AFP determination. About the reported case, the chronology of facts is unusual: ultrasonography led initially to suspect anomaly, then elevated AFP result confirmed the malformation. 相似文献
107.
Palumbo E Favier CF Deghorain M Cocconcelli PS Grangette C Mercenier A Vaughan EE Hols P 《FEMS microbiology letters》2004,239(1):131-138
A stable mutant of Lactobacillus plantarum deficient in alanine racemase (Alr) was constructed by two successive homologous recombination steps. When the mutant was supplemented with D-alanine, growth and viability were unaffected. Surprisingly, deprivation of d-alanine during exponential growth did not result in a rapid and extensive lysis as observed in Alr-deficient strains of Escherichia coli or Bacillus subtilis. Rather, the starved mutant cells underwent a growth arrest and were gradually affected in viability with a decrease in colony forming units over 99% in less than 24 h. Additionally, fluorescent techniques demonstrated a loss of cell envelope integrity in the starved cells. Prolonged d-alanine starvation resulted in cells with an aberrant morphology. Scanning and transmission electron microscopy analyses revealed an increase in cell length, deficiencies in septum formation, thinning of the cell envelope and perforation of the cell wall in the septum region. We discuss the involvement of peptidoglycan hydrolases in these phenotypic defects in the context of the crucial role played by D-alanine in peptidoglycan biosynthesis and teichoic acids substitution. 相似文献
108.
109.
Vascular smooth muscle contracts on increases of extracellular pH (pH(o)) and relaxes on pH(o) decreases possibly resulting from changes in transsarcolemmal Ca(2+) influx. Therefore, we studied store-operated Ca(2+) entry (SOCE; i.e. capacitative Ca(2+) entry (CCE)) during acidification (pH(o)=6.5) and alkalinization (pH(o)=8.0) in isolated porcine coronary smooth muscle cells (SMCs) by monitoring cytoplasmic Ca(2+) ([Ca(2+)](i)) and divalent cation entry (Mn(2+) quench) with fura-2/AM-fluorometry. Additionally, we evaluated the contribution of SOCE to pH(o)-dependent changes in isometric tension of porcine coronary smooth muscle strips. SOCE elicited in SMCs by the SERCA inhibitor BHQ was strongly modulated by pH(o) showing a decrease upon acidification and vice versa an increase upon alkalinization. BHQ-mediated tension of smooth muscle strips also revealed strong pH(o) dependence. In contrast, L-VOC-dependent tension ([K(+)](o)=20 and 40 mmol l(-1)) was remarkably less affected by pH(o) changes. Moreover, refilling of depleted Ca(2+) stores after repeated M(3)-cholinergic receptor stimulation could be almost completely inhibited by SKF 96365 and was markedly reduced by acidification and considerably enhanced by alkalinization pointing to a major role of SOCE in refilling. We conclude that vascular tone particularly responds to alterations in pH(o) whenever SOCE substantially contributes to the amount of activator Ca(2+) for contraction. 相似文献
110.
Lorthiois E Bernardelli P Vergne F Oliveira C Mafroud AK Proust E Heuze L Moreau F Idrissi M Tertre A Bertin B Coupe M Wrigglesworth R Descours A Soulard P Berna P 《Bioorganic & medicinal chemistry letters》2004,14(18):4623-4626
The synthesis and SAR studies of spiroquinazolinones as novel PDE7 inhibitors are discussed. The best compounds from the series displayed nanomolar inhibitory affinity and were selective versus other PDE isoenzymes. 相似文献