全文获取类型
收费全文 | 174992篇 |
免费 | 12131篇 |
国内免费 | 42篇 |
专业分类
187165篇 |
出版年
2021年 | 1737篇 |
2020年 | 1402篇 |
2019年 | 1498篇 |
2018年 | 3428篇 |
2017年 | 3093篇 |
2016年 | 4174篇 |
2015年 | 5069篇 |
2014年 | 5489篇 |
2013年 | 7503篇 |
2012年 | 8511篇 |
2011年 | 7970篇 |
2010年 | 5513篇 |
2009年 | 4331篇 |
2008年 | 6779篇 |
2007年 | 6503篇 |
2006年 | 6309篇 |
2005年 | 5572篇 |
2004年 | 5556篇 |
2003年 | 5135篇 |
2002年 | 4757篇 |
2001年 | 6312篇 |
2000年 | 5934篇 |
1999年 | 4589篇 |
1998年 | 1645篇 |
1997年 | 1466篇 |
1996年 | 1405篇 |
1992年 | 3306篇 |
1991年 | 3248篇 |
1990年 | 3239篇 |
1989年 | 3035篇 |
1988年 | 2758篇 |
1987年 | 2701篇 |
1986年 | 2468篇 |
1985年 | 2535篇 |
1984年 | 2103篇 |
1983年 | 1816篇 |
1982年 | 1370篇 |
1979年 | 2064篇 |
1978年 | 1599篇 |
1977年 | 1477篇 |
1976年 | 1386篇 |
1975年 | 1698篇 |
1974年 | 1832篇 |
1973年 | 1897篇 |
1972年 | 1700篇 |
1971年 | 1507篇 |
1970年 | 1420篇 |
1969年 | 1530篇 |
1968年 | 1369篇 |
1967年 | 1277篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Systematic procedures for calculating inbreeding coefficients 总被引:4,自引:0,他引:4
82.
The capillaries of the cardiac muscle were investigated in the goat by means of light microscopy, transmission electron microscopy and scanning electron microscopy, and the following results were obtained. The capillaries of the working cardiac muscles were numerous, arranged mainly parallel to the long axis of muscle cells and formed dense elongated networks. On the contrary, those of the terminal Purkinje fibers were relatively few in number, oriented in various directions and formed loose and circularly meshed networks surrounding the fibers. Such findings were discussed in correlation with the physiology and functional morphology of various types of the cardiac muscle cells. 相似文献
83.
84.
85.
A computer simulation model was developed to investigate nitrogenfluxes associated with microbial interactions in plankton communities.A short time scale was used, appropriate to the build-up anddecline of phytoplankton blooms in temperate shelf waters aftera mixing or upwelling event. The model depicts a continuum ofevents, many of which have been observed in coastal, upwellingand oceanic systems, including two phytoplankton peaks correspondingto new production and regenerated production.It predicts that nitrogen loss through sedimentation of phytoplanktonand faeces may result in a smaller bloom with a delayed onsetand prolonged duration. Microbial regeneration of nitrogen wasfound to be important in sustaining the middle stages of a phytoplanktonbloom, whereas micro- and meso-zooplankton regeneration occurredtowards the end of the bloom. 相似文献
86.
I Gut J Nerudová A Stiborová J Kopecky E Frantík 《Journal of hygiene, epidemiology, microbiology, and immunology》1985,29(1):9-13
In male Wistar rats, the inhalation exposure to acrylonitrile (AN), 271 mg X m-3, 8 hours a day, 5 days a week, did not affect protein sulfhydryl concentration in liver and blood and decreased glutathione concentration in the liver, but not in the brain at the end of the fifth exposure. The urinary excretion of the main AN metabolites, thioethers (AN-mercapturic acids) and thiocyanate was proportional to the inhaled AN concentration (57, 125, 271 mg X m-3, respectively) in a single exposure for 12 hours, and their mutual ratio was greatly different from that after injection of AN. The results revealed that the urinary excretion of thioethers is a very sensitive and dose-related indicator of exposure to AN and extrapolation of the results indicates that the exposure to AN concentration below 10 mg X m-3 could thus be demonstrated. 相似文献
87.
88.
V. S. Oganov O. L. Vinogradova N. S. Dudov V. S. Baranov A. S. Minenkov A. V. Bakulin V. E. Novikov O. E. Kabitskaya M. V. Moskalenko A. S. Glotov O. S. Glotov D. V. Popov 《Human physiology》2008,34(2):182-190
The association of the polymorphism of the VDR, Col1a1, and CALCR genes with a form of osteoporosis frequently occurring as a consequence of intense physical exercise in athletes was studied. Biochemical parameters of bone remodeling and its neuroendocrine regulation, as well as the bone masses, of 22 amateur athletes were determined immediately before a strenuous nine-week training cycle (TC) and eight months later. The possible association of these factors with the polymorphism of the genes coding for bone tissue proteins was studied. Long-term intense physical training was found to be associated with a significant activation of bone tissue resorption accompanied by continued rapid synthesis. Nevertheless, and in spite of the strong activation of resorption caused by the TC, the athletes exhibited no osteoporosis (even eight months after the discontinuation of the TC); some of them, however, displayed an individual tendency to osteopenia. According to the results of genetic analysis, this was associated with the polymorphism of predisposition genes (genotype TT of the VDR gene and the functionally weakened s allele of the Col1a1 gene). 相似文献
89.
Li Zhang Mark Morrison Páraic ó Cuív Paul Evans Claire M. Rickard 《Journal of bacteriology》2012,194(23):6639
In recent years, Staphylococcus epidermidis has become a major nosocomial pathogen and the most common cause of intravascular catheter-related bacteremia, which can increase morbidity and mortality and significantly affect patient recovery. We report a draft genome sequence of Staphylococcus epidermidis AU12-03, isolated from an intravascular catheter tip. 相似文献
90.
Larisa R. G. DeSantis Jessica R. Scott Blaine W. Schubert Shelly L. Donohue Brian M. McCray Courtney A. Van Stolk Amanda A. Winburn Michael A. Greshko Mackie C. O’Hara 《PloS one》2013,8(8)
The analysis of dental microwear is commonly used by paleontologists and anthropologists to clarify the diets of extinct species, including herbivorous and carnivorous mammals. Currently, there are numerous methods employed to quantify dental microwear, varying in the types of microscopes used, magnifications, and the characterization of wear in both two dimensions and three dimensions. Results from dental microwear studies utilizing different methods are not directly comparable and human quantification of wear features (e.g., pits and scratches) introduces interobserver error, with higher error being produced by less experienced individuals. Dental microwear texture analysis (DMTA), which analyzes microwear features in three dimensions, alleviates some of the problems surrounding two-dimensional microwear methods by reducing observer bias. Here, we assess the accuracy and comparability within and between 2D and 3D dental microwear analyses in herbivorous and carnivorous mammals at the same magnification. Specifically, we compare observer-generated 2D microwear data from photosimulations of the identical scanned areas of DMTA in extant African bovids and carnivorans using a scanning white light confocal microscope at 100x magnification. Using this magnification, dental microwear features quantified in 2D were able to separate grazing and frugivorous bovids using scratch frequency; however, DMTA variables were better able to discriminate between disparate dietary niches in both carnivorous and herbivorous mammals. Further, results demonstrate significant interobserver differences in 2D microwear data, with the microwear index remaining the least variable between experienced observers, consistent with prior research. Overall, our results highlight the importance of reducing observer error and analyzing dental microwear in three dimensions in order to consistently interpret diets accurately. 相似文献