全文获取类型
收费全文 | 6974篇 |
免费 | 617篇 |
国内免费 | 1篇 |
出版年
2021年 | 84篇 |
2020年 | 62篇 |
2019年 | 66篇 |
2018年 | 75篇 |
2017年 | 84篇 |
2016年 | 143篇 |
2015年 | 243篇 |
2014年 | 276篇 |
2013年 | 317篇 |
2012年 | 447篇 |
2011年 | 450篇 |
2010年 | 294篇 |
2009年 | 258篇 |
2008年 | 386篇 |
2007年 | 381篇 |
2006年 | 351篇 |
2005年 | 368篇 |
2004年 | 322篇 |
2003年 | 349篇 |
2002年 | 334篇 |
2001年 | 144篇 |
2000年 | 112篇 |
1999年 | 129篇 |
1998年 | 112篇 |
1997年 | 90篇 |
1996年 | 72篇 |
1995年 | 57篇 |
1994年 | 66篇 |
1993年 | 71篇 |
1992年 | 100篇 |
1991年 | 84篇 |
1990年 | 79篇 |
1989年 | 76篇 |
1988年 | 83篇 |
1987年 | 75篇 |
1986年 | 47篇 |
1985年 | 82篇 |
1984年 | 76篇 |
1983年 | 55篇 |
1982年 | 51篇 |
1981年 | 59篇 |
1980年 | 50篇 |
1979年 | 38篇 |
1978年 | 44篇 |
1977年 | 44篇 |
1976年 | 26篇 |
1975年 | 26篇 |
1974年 | 34篇 |
1973年 | 19篇 |
1972年 | 16篇 |
排序方式: 共有7592条查询结果,搜索用时 15 毫秒
1.
2.
P Salgame A S Varadhachary L L Primiano J E Fincke S Muller M Monestier 《Nucleic acids research》1997,25(3):680-681
We describe a simple and convenient enzyme-linked immunosorbent assay (ELISA) for the detection of apoptosis in tissue culture. An early event in apoptosis is DNA fragmentation followed by release of nucleosomes into the cytoplasm. Our sandwich assay uses a pair of monoclonal antibodies specific for two nucleosomal epitopes to capture and detect cytoplasmic nucleosomes onto the ELISA plate. Our assay is about 500 times more sensitive than the detection of apoptotic DNA ladder by agarose electrophoresis and is especially suited for the testing of large numbers of samples. 相似文献
3.
China has recently made available hourly air pollution data from over 1500 sites, including airborne particulate matter (PM), SO2, NO2, and O3. We apply Kriging interpolation to four months of data to derive pollution maps for eastern China. Consistent with prior findings, the greatest pollution occurs in the east, but significant levels are widespread across northern and central China and are not limited to major cities or geologic basins. Sources of pollution are widespread, but are particularly intense in a northeast corridor that extends from near Shanghai to north of Beijing. During our analysis period, 92% of the population of China experienced >120 hours of unhealthy air (US EPA standard), and 38% experienced average concentrations that were unhealthy. China’s population-weighted average exposure to PM2.5 was 52 μg/m3. The observed air pollution is calculated to contribute to 1.6 million deaths/year in China [0.7–2.2 million deaths/year at 95% confidence], roughly 17% of all deaths in China. 相似文献
4.
Nathalie Jeanray Rapha?l Marée Benoist Pruvot Olivier Stern Pierre Geurts Louis Wehenkel Marc Muller 《PloS one》2015,10(1)
Zebrafish is increasingly used to assess biological properties of chemical substances and thus is becoming a specific tool for toxicological and pharmacological studies. The effects of chemical substances on embryo survival and development are generally evaluated manually through microscopic observation by an expert and documented by several typical photographs. Here, we present a methodology to automatically classify brightfield images of wildtype zebrafish embryos according to their defects by using an image analysis approach based on supervised machine learning. We show that, compared to manual classification, automatic classification results in 90 to 100% agreement with consensus voting of biological experts in nine out of eleven considered defects in 3 days old zebrafish larvae. Automation of the analysis and classification of zebrafish embryo pictures reduces the workload and time required for the biological expert and increases the reproducibility and objectivity of this classification. 相似文献
5.
Julia Reiss Jon R. Bridle Jos M. Montoya Guy Woodward 《Trends in ecology & evolution》2009,24(9):505-514
6.
Werner E.C. Muller Jürgen Conrad Rudolf K. Zahn Renate Steffen Gerhard Uhlenbruck Isabel Miller 《Differentiation; research in biological diversity》1984,26(1-3):30-35
Abstract. The Hexactinellida sponge Aphrocallistes vastus contains a soluble aggregation factor (AF) whose purification has been described in this communication. It is characterized by a S°20.w value of 37 and a buoyant density of 1.45 g/cm3 . The AF is a glycoporteinaceous particle composed of three major protein species; no core structure could be visualized. In the presence of Ca2+ , the AF causes secondary aggregation of single cells. The aggregation process is temperature, pH, and ionic strength independent within a broad range. Evidence is presented indicating that two (or more) AF molecules are required for the establishment of a stable cell: cell interaction. In contrast to the AFs from demosponges, the hexactinellid AF functions species-unspecifically. 相似文献
7.
Physiological states of mitochondria often correlate with distinctive morphology. Electron microscopy and tomographic reconstruction were used to investigate the three-dimensional structure of axonal mitochondria and mitochondria in the surrounding Schwann cells of the peripheral nervous system (PNS), both in the vicinity of nodes of Ranvier and far from these nodes. Condensed mitochondria were found to be abundant in the axoplasm, but not in the Schwann cell. Uncharacteristic of the classical morphology of condensed mitochondria, the outer and inner boundary membranes are in close apposition and the crista junctions are narrow, consistent with their function as gates for the diffusion of macromolecules. There is also less cristae surface area and lower density of crista junctions in these mitochondria. The density of mitochondria was greater at the paranode–node–paranode (PNP) as was the crista junction opening, yet there were fewer cristae in these organelles compared to those in the internodal region. The greater density of condensed mitochondria in the PNS axoplasm and in particular at the PNP suggests a need for these organelles to operate at a high workload of ATP production. 相似文献
8.
9.
10.
K Elwin R M Chalmers R Roberts E C Guy D P Casemore 《Applied and environmental microbiology》2001,67(12):5581-5584
The application of genotyping to clinical isolates of Cryptosporidium has increased significantly our knowledge and understanding of the distribution and epidemiology of this parasite. However, some methods can be laborious and demand specialist technical expertise. PCR-restriction fragment length polymorphism (RFLP) techniques represent a more rapid and simple method of genotyping to support epidemiological and clinical investigations than conventional DNA analytical techniques. We describe a nested PCR-RFLP technique that identifies polymorphisms in the C. parvum thrombospondin-related adhesive protein gene locus; this method offers a sensitive and specific tool for the confirmation and investigation of disease associated with C. parvum. The potential of this enhanced method is demonstrated by its application to the confirmation and epidemiological investigation of an outbreak of cryptosporidiosis associated with a school visit to an open farm. 相似文献