全文获取类型
收费全文 | 24179篇 |
免费 | 2090篇 |
国内免费 | 20篇 |
专业分类
26289篇 |
出版年
2021年 | 271篇 |
2020年 | 202篇 |
2019年 | 229篇 |
2018年 | 264篇 |
2017年 | 268篇 |
2016年 | 400篇 |
2015年 | 666篇 |
2014年 | 700篇 |
2013年 | 995篇 |
2012年 | 1102篇 |
2011年 | 1123篇 |
2010年 | 861篇 |
2009年 | 679篇 |
2008年 | 856篇 |
2007年 | 888篇 |
2006年 | 844篇 |
2005年 | 840篇 |
2004年 | 949篇 |
2003年 | 881篇 |
2002年 | 825篇 |
2001年 | 697篇 |
2000年 | 687篇 |
1999年 | 650篇 |
1998年 | 335篇 |
1997年 | 349篇 |
1996年 | 347篇 |
1995年 | 306篇 |
1994年 | 250篇 |
1993年 | 280篇 |
1992年 | 596篇 |
1991年 | 489篇 |
1990年 | 529篇 |
1989年 | 527篇 |
1988年 | 430篇 |
1987年 | 432篇 |
1986年 | 379篇 |
1985年 | 380篇 |
1984年 | 405篇 |
1983年 | 312篇 |
1982年 | 285篇 |
1981年 | 274篇 |
1980年 | 244篇 |
1979年 | 328篇 |
1978年 | 266篇 |
1977年 | 282篇 |
1976年 | 213篇 |
1975年 | 235篇 |
1974年 | 240篇 |
1973年 | 210篇 |
1971年 | 182篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
Dorothea Bedigian Sebsebe Demissew Paul Gepts Daniel F. Austin Neil A. Harriman John Klock Sarah Walshaw John Richard Stepp Beverly J. Brown Julie Polley David Winston Barbara Pickersgill Patrick Van Damme Nina L. Etkin Beronda L. Montgomery Linda Perry Stephen E Siebert Robert J. Krueger Kathleen McConnell Wendy Applequist Mary Theresa Bonhage-Freund Karol Chandler-Ezell 《Economic botany》2005,59(4):395-412
3.
The Scheldt estuary: a description of a changing ecosystem 总被引:2,自引:0,他引:2
Patrick Meire Tom Ysebaert Stefan Van Damme Erika Van den Bergh Tom Maris Eric Struyf 《Hydrobiologia》2005,540(1-3):1-11
4.
M Dreyer R Prager A Robinson K Busch G Ellis E Souhami R Van Leendert 《Hormones et métabolisme》2005,37(11):702-707
Insulin glulisine (glulisine), a human insulin analogue with a rapid-acting time-action profile, has been developed to fulfil the mealtime (bolus) insulin requirement in patients with diabetes. The aim of this multinational, multi-centre, controlled, open-label, randomized, parallel-group study was to compare the efficacy and safety of insulin glulisine (glulisine) to that of insulin lispro (lispro) in adults diagnosed with Type 1 diabetes. Of the 683 patients randomized, 672 received treatment (339 patients received glulisine, 333 patients received lispro). Over the 26-week study, a similar reduction in mean HbA1c occurred in both groups (adjusted mean change from baseline -0.14% in both groups). The basal insulin dose was relatively unchanged from baseline in the glulisine group but increased in the lispro group (glulisine: 0.12 IU vs. lispro: 1.82 IU; p = 0.0001). As a consequence, total daily insulin dose decreased in the glulisine group but increased in the lispro group (glulisine: -0.86 IU vs. lispro: 1.01 IU; p = 0.0123). There was no relevant difference between the two groups in the reporting of symptomatic hypoglycaemia (overall, nocturnal and severe). This study demonstrates that glulisine provides equivalent glycaemic control to lispro. The clinical relevance of any difference in total daily insulin dose remains to be established. 相似文献
5.
An Exploratory Framework for the Empirical Measurement of Resilience 总被引:12,自引:1,他引:11
G. S. Cumming G. Barnes S. Perz M. Schmink K. E. Sieving J. Southworth M. Binford R. D. Holt C. Stickler T. Van Holt 《Ecosystems》2005,8(8):975-987
Deliberate progress towards the goal of long-term sustainability depends on understanding the dynamics of linked social and
ecological systems. The concept of social-ecological resilience holds promise for interdisciplinary syntheses. Resilience
is a multifaceted concept that as yet has not been directly operationalized, particularly in systems for which our ignorance
is such that detailed, parameter-rich simulation models are difficult to develop. We present an exploratory framework as a
step towards the operationalization of resilience for empirical studies. We equate resilience with the ability of a system
to maintain its identity, where system identity is defined as a property of key components and relationships (networks) and
their continuity through space and time. Innovation and memory are also fundamental to understanding identity and resilience.
By parsing our systems into the elements that we subjectively consider essential to identity, we obtain a small set of specific
focal variables that reflect changes in identity. By assessing the potential for changes in identity under specified drivers
and perturbations, in combination with a scenario-based approach to considering alternative futures, we obtain a surrogate
measure of the current resilience of our study system as the likelihood of a change in system identity under clearly specified
conditions, assumptions, drivers and perturbations. Although the details of individual case studies differ, the concept of
identity provides a level of generality that can be used to compare measure of resilience across cases. Our approach will
also yield insights into the mechanisms of change and the potential consequences of different policy and management decisions,
providing a level of decision support for each case study area. 相似文献
6.
7.
Studies of the Extracellular Glycocalyx of the Anaerobic Cellulolytic Bacterium Ruminococcus albus 7
下载免费PDF全文
![点击此处可从《Applied microbiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Paul J. Weimer Neil P. J. Price Otini Kroukamp Lydia-Marie Joubert Gideon M. Wolfaardt Willem H. Van Zyl 《Applied microbiology》2006,72(12):7559-7566
Anaerobic cellulolytic bacteria are thought to adhere to cellulose via several mechanisms, including production of a glycocalyx containing extracellular polymeric substances (EPS). As the compositions and structures of these glycocalyces have not been elucidated, variable-pressure scanning electron microscopy (VP-SEM) and chemical analysis were used to characterize the glycocalyx of the ruminal bacterium Ruminococcus albus strain 7. VP-SEM revealed that growth of this strain was accompanied by the formation of thin cellular extensions that allowed the bacterium to adhere to cellulose, followed by formation of a ramifying network that interconnected individual cells to one another and to the unraveling cellulose microfibrils. Extraction of 48-h-old whole-culture pellets (bacterial cells plus glycocalyx [G] plus residual cellulose [C]) with 0.1 N NaOH released carbohydrate and protein in a ratio of 1:5. Boiling of the cellulose fermentation residue in a neutral detergent solution removed almost all of the adherent cells and protein while retaining a residual network of adhering noncellular material. Trifluoroacetic acid hydrolysis of this residue (G plus C) released primarily glucose, along with substantial amounts of xylose and mannose, but only traces of galactose, the most abundant sugar in most characterized bacterial exopolysaccharides. Linkage analysis and characterization by nuclear magnetic resonance suggested that most of the glucosyl units were not present as partially degraded cellulose. Calculations suggested that the energy demand for synthesis of the nonprotein fraction of EPS by this organism represents only a small fraction (<4%) of the anabolic ATP expenditure of the bacterium. 相似文献
8.
9.
10.
Van Anthony M. Villar John Edward Jones Ines Armando Laureano D. Asico Crisanto S. Escano Jr. Hewang Lee Xiaoyan Wang Yu Yang Annabelle M. Pascua-Crusan Cynthia P. Palmes-Saloma Robin A. Felder Pedro A. Jose 《The Journal of biological chemistry》2013,288(1):152-163
The peripheral dopaminergic system plays a crucial role in blood pressure regulation through its actions on renal hemodynamics and epithelial ion transport. The dopamine D5 receptor (D5R) interacts with sorting nexin 1 (SNX1), a protein involved in receptor retrieval from the trans-Golgi network. In this report, we elucidated the spatial, temporal, and functional significance of this interaction in human renal proximal tubule cells and HEK293 cells stably expressing human D5R and in mice. Silencing of SNX1 expression via RNAi resulted in the failure of D5R to internalize and bind GTP, blunting of the agonist-induced increase in cAMP production and decrease in sodium transport, and up-regulation of angiotensin II receptor expression, of which expression was previously shown to be negatively regulated by D5R. Moreover, siRNA-mediated depletion of renal SNX1 in C57BL/6J and BALB/cJ mice resulted in increased blood pressure and blunted natriuretic response to agonist in salt-loaded BALB/cJ mice. These data demonstrate a crucial role for SNX1 in D5R trafficking and that SNX1 depletion results in D5R dysfunction and thus may represent a novel mechanism for the pathogenesis of essential hypertension. 相似文献