全文获取类型
收费全文 | 11414篇 |
免费 | 1249篇 |
国内免费 | 3篇 |
专业分类
12666篇 |
出版年
2021年 | 148篇 |
2020年 | 91篇 |
2019年 | 126篇 |
2018年 | 142篇 |
2017年 | 127篇 |
2016年 | 241篇 |
2015年 | 363篇 |
2014年 | 421篇 |
2013年 | 539篇 |
2012年 | 597篇 |
2011年 | 635篇 |
2010年 | 393篇 |
2009年 | 385篇 |
2008年 | 530篇 |
2007年 | 551篇 |
2006年 | 488篇 |
2005年 | 452篇 |
2004年 | 461篇 |
2003年 | 444篇 |
2002年 | 432篇 |
2001年 | 248篇 |
2000年 | 257篇 |
1999年 | 244篇 |
1998年 | 159篇 |
1997年 | 141篇 |
1996年 | 162篇 |
1995年 | 120篇 |
1994年 | 119篇 |
1993年 | 142篇 |
1992年 | 197篇 |
1991年 | 200篇 |
1990年 | 204篇 |
1989年 | 149篇 |
1988年 | 116篇 |
1987年 | 140篇 |
1986年 | 128篇 |
1985年 | 167篇 |
1984年 | 134篇 |
1983年 | 127篇 |
1982年 | 111篇 |
1981年 | 108篇 |
1980年 | 108篇 |
1979年 | 96篇 |
1978年 | 94篇 |
1977年 | 84篇 |
1976年 | 76篇 |
1975年 | 94篇 |
1974年 | 83篇 |
1973年 | 85篇 |
1972年 | 70篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
131.
A histochemical study has been made on the myotomal musculature of the rainbow trout Salmo gairdneri Richardson. Four main types of fibre can be distinguished on the basis of differences in fibre size, lipid content and succinic dehydrogenase and myofibrillar adenosine triphosphatase activity (ATPase activity). Early histological studies have concluded that in addition to a superficial strip of muscle small diameter 'red' fibres occur throughout the trout myotome. These small diameter fibres occurring in the bulk of the myotome are shown to differ from the superficial fibres with respect to their oxidative metabolism and myofibrillar ATPase. The relevance of this finding to studies on the energetics and swimming efficiency of this species are discussed. 相似文献
132.
133.
The location of proteins labeled by the 125I-lactoperoxidase system in the NIL 8 hamster fibroblast. 总被引:17,自引:0,他引:17
NIL 8 hamster fibroblast cells were labeled by lactoperoxidase-catalyzed iodination. Their membranes were fractionated by sedimentation-rate and isopycnic zonal centrifugation. All the iodinated proteins except the very prominently labeled high molecular weight protein (greater than 200,000 daltons) were located in a fraction identified enzymically and compositionally as plasma membrane. The high molecular weight protein that was previously shown to be sensitive to virus transformation (Hynes, 1973) is concentrated in a very high density particle (rho equals 1.253-1.259) which contains mainly carbohydrate and protein and very low levels of lipid. 5'-nucleotidase was the only enzyme reproducibly demonstrated in this fraction, and electron micrographs revealed a predominantly amorphous morphology together with a few membraneous structures. The iodine label in this fraction was very sensitive to trypsinization prior to homogenization. All the available evidence indicates that this fraction is derived from the surface coat. Mitochondria, nuclei, and soluble protein were labeled to an insignificant extent. The presence of the iodinated surface proteins associated with the endoplasmic reticulum fraction is discussed in the light of these results. 相似文献
134.
Paired oral and intravenous glucose tolerance tests were carried out in patients who had undergone truncal vagotomy and pyloroplasty, selective vagotomy and pyloroplasty, or highly selective vagotomy at least six months earlier. Intravenous glucose tolerance was similar in all three groups. Oral glucose elicited significantly higher concentrations of plasma insulin in patients who had undergone selective and highly selective vagotomy than in those treated by truncal vagotomy. When the same amount of glucose was given intravenously, however, plasma insulin concentrations were similar in all three groups of patients. The insulin secreted in response to intravenous glucose expressed as a percentage of that secreted in response to oral glucose was 112% for truncal vagotomy, 51% for selective vagotomy, and 52% for highly selective vagotomy. Truncal vagotomy thus led to a diminished insulin response to oral glucose, which was probably due to impaired release of small-bowel hormones. 相似文献
135.
Uterine response to inoculation with Streptococcus zooepidemicus organisms (antigenic markers) and 15-mum microspheres and charcoal (non - antigenic markers) was determined in seasonally acyclic maiden mares treated with either progesterone (P) n = 4, estradiol (E) n = 4 or oil vehicle (C) n = 4. At 3, 7 and 15 d after inoculation with bacteria and the 2 non - antigenic markers, uteri were flushed and the clearance of these materials, as well as the number of white blood cells and immunoglobulin concentration, determined. P-treated mares had higher numbers of bacteria and IgA and a greater volume of purulent fluid in the uterus than E- or C-treated mares at 7 d after inoculation. Clearance of inoculated materials began within 2 h in E-treated mares, and the non-antigenic markers were completely cleared in E- and C-, but not in P-treated mares, in 3 d. This suggests that in the P-dominated uterus, reduced physical clearance may contribute to an increased susceptibility to uterine infection. 相似文献
136.
Hiwa Majed Tatiana Johnston Celine Kelso Enrico Monachino Slobodan Jergic Nicholas E. Dixon Eleftherios Mylonakis Michael J. Kelso 《Bioorganic & medicinal chemistry letters》2018,28(22):3526-3528
Methicillin-resistant Staphylococcus aureus (MRSA) is a major cause of serious hospital-acquired infections and is responsible for significant morbidity and mortality in residential care facilities. New agents against MRSA are needed to combat rising resistance to current antibiotics. We recently reported 5-hydroxy-3-methyl-1-phenyl-1H-pyrazole-4-carbodithioate (HMPC) as a new bacteriostatic agent against MRSA that appears to act via a novel mechanism. Here, twenty nine analogs of HMPC were synthesized, their anti-MRSA structure-activity relationships evaluated and selectivity versus human HKC-8 cells determined. Minimum inhibitory concentrations (MIC) ranged from 0.5 to 64?μg/mL and up to 16-fold selectivity was achieved. The 4-carbodithioate function was found to be essential for activity but non-specific reactivity was ruled out as a contributor to antibacterial action. The study supports further work aimed at elucidating the molecular targets of this interesting new class of anti-MRSA agents. 相似文献
137.
138.
Rumi Zhang Peiyu Zhang Colin Dalton Graham A. Jullien 《Biomechanics and modeling in mechanobiology》2010,9(1):77-86
In this paper, we apply mixture theory to quantitatively predict the transient behavior of drug delivery by using a microneedle
array inserted into tissue. In the framework of mixture theory, biological tissue is treated as a multi-phase fluid saturated
porous medium, where the mathematical behavior of the tissue is characterized by the conservation equations of multi-phase
models. Drug delivery by microneedle array imposes additional requirements on the simulation procedures, including drug absorption
by the blood capillaries and tissue cells, as well as a moving interface along its flowing pathway. The contribution of this
paper is to combine mixture theory with the moving mesh methods in modeling the transient behavior of drug delivery into tissue.
Numerical simulations are provided to obtain drug concentration distributions into tissues and capillaries. 相似文献
139.
Istem Fer Anthony K. Gardella Alexey N. Shiklomanov Eleanor E. Campbell Elizabeth M. Cowdery Martin G. De Kauwe Ankur Desai Matthew J. Duveneck Joshua B. Fisher Katherine D. Haynes Forrest M. Hoffman Miriam R. Johnston Rob Kooper David S. LeBauer Joshua Mantooth William J. Parton Benjamin Poulter Tristan Quaife Ann Raiho Kevin Schaefer Shawn P. Serbin James Simkins Kevin R. Wilcox Toni Viskari Michael C. Dietze 《Global Change Biology》2021,27(1):13-26
In an era of rapid global change, our ability to understand and predict Earth's natural systems is lagging behind our ability to monitor and measure changes in the biosphere. Bottlenecks to informing models with observations have reduced our capacity to fully exploit the growing volume and variety of available data. Here, we take a critical look at the information infrastructure that connects ecosystem modeling and measurement efforts, and propose a roadmap to community cyberinfrastructure development that can reduce the divisions between empirical research and modeling and accelerate the pace of discovery. A new era of data‐model integration requires investment in accessible, scalable, and transparent tools that integrate the expertise of the whole community, including both modelers and empiricists. This roadmap focuses on five key opportunities for community tools: the underlying foundations of community cyberinfrastructure; data ingest; calibration of models to data; model‐data benchmarking; and data assimilation and ecological forecasting. This community‐driven approach is a key to meeting the pressing needs of science and society in the 21st century. 相似文献
140.
Spider dragline silk is a self-assembling tunable protein composite fiber that rivals many engineering fibers in tensile strength, extensibility, and toughness, making it one of the most versatile biocompatible materials and most inviting for synthetic mimicry. While experimental studies have shown that the peptide sequence and molecular structure of silk have a direct influence on the stiffness, toughness, and failure strength of silk, few molecular-level analyses of the nanostructure of silk assemblies, in particular, under variations of genetic sequences have been reported. In this study, atomistic-level structures of wildtype as well as modified MaSp1 protein from the Nephila clavipes spider dragline silk sequences, obtained using an in silico approach based on replica exchange molecular dynamics and explicit water molecular dynamics, are subjected to simulated nanomechanical testing using different force-control loading conditions including stretch, pull-out, and peel. The authors have explored the effects of the poly-alanine length of the N. clavipes MaSp1 peptide sequence and identify differences in nanomechanical loading conditions on the behavior of a unit cell of 15 strands with 840-990 total residues used to represent a cross-linking β-sheet crystal node in the network within a fibril of the dragline silk thread. The specific loading condition used, representing concepts derived from the protein network connectivity at larger scales, have a significant effect on the mechanical behavior. Our analysis incorporates stretching, pull-out, and peel testing to connect biochemical features to mechanical behavior. The method used in this study could find broad applications in de novo design of silk-like tunable materials for an array of applications. 相似文献