全文获取类型
收费全文 | 5525篇 |
免费 | 612篇 |
国内免费 | 2篇 |
出版年
2022年 | 34篇 |
2021年 | 66篇 |
2020年 | 53篇 |
2019年 | 55篇 |
2018年 | 74篇 |
2017年 | 68篇 |
2016年 | 114篇 |
2015年 | 213篇 |
2014年 | 237篇 |
2013年 | 256篇 |
2012年 | 352篇 |
2011年 | 338篇 |
2010年 | 219篇 |
2009年 | 195篇 |
2008年 | 306篇 |
2007年 | 311篇 |
2006年 | 322篇 |
2005年 | 277篇 |
2004年 | 293篇 |
2003年 | 251篇 |
2002年 | 255篇 |
2001年 | 110篇 |
2000年 | 122篇 |
1999年 | 117篇 |
1998年 | 92篇 |
1997年 | 63篇 |
1996年 | 61篇 |
1995年 | 52篇 |
1994年 | 65篇 |
1993年 | 69篇 |
1992年 | 96篇 |
1991年 | 74篇 |
1990年 | 67篇 |
1989年 | 76篇 |
1988年 | 74篇 |
1987年 | 57篇 |
1986年 | 52篇 |
1985年 | 55篇 |
1984年 | 43篇 |
1983年 | 45篇 |
1982年 | 35篇 |
1981年 | 31篇 |
1980年 | 24篇 |
1979年 | 30篇 |
1978年 | 23篇 |
1977年 | 27篇 |
1976年 | 39篇 |
1975年 | 23篇 |
1973年 | 26篇 |
1972年 | 22篇 |
排序方式: 共有6139条查询结果,搜索用时 31 毫秒
1.
Phenylobacterium immobile, a bacterium which is able to degrade the herbicide chloridazon, utilizes for L-tyrosine synthesis arogenate as an obligatory intermediate which is converted in the final biosynthetic step by a dehydrogenase to tyrosine. This enzyme, the arogenate dehydrogenase, has been purified for the first time in a 5-step procedure to homogeneity as confirmed by electrophoresis. The Mr of the enzyme that consists of two identical subunits amounts to 69000 as established by gel electrophoresis after cross-linking the enzyme with dimethylsuberimidate. The Km values were 0.09 mM for arogenate and 0.02 mM for NAD+. The enzyme has a high specificity with respect to its substrate arogenate. 相似文献
2.
Amino acid sulfur as a source of sulfate for sulfated proteoglycans produced by Swiss mouse 3T3 cells 总被引:3,自引:0,他引:3
The uptake of sulfate by Swiss mouse 3T3 cells is blocked in the presence of 1 mM 4-isothiocyano-4'-acetamido-stilbene-2,2-disulfonic acid (SITS). In the absence of an exogenous source of sulfate, glycosaminoglycans produced by cells in the presence of the inhibitor are sulfated to the same extent as those produced by cells grown in its absence. The sulfate utilized in the absence of medium sulfate has been identified as that produced by the oxidation of the sulfur present in the amino acids cysteine and methionine. This finding indicates that, under conditions of restricted exogenous sulfate, caution is needed in the interpretation of data obtained with the use of [35S]methionine and/or [35S]cysteine as a general protein label, since both tyrosine and a variety of types of protein-linked carbohydrate chains may be modified by sulfation. 相似文献
3.
Viscoelasticity of packed erythrocyte suspensions subjected to low amplitude oscillatory deformation.
下载免费PDF全文
![点击此处可从《Biophysical journal》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Concentrated adult erythrocyte suspensions were subjected to low amplitude oscillatory shear in a Weissenberg rheogoniometer equipped with a cone-and-plate assembly. The dynamic viscoelastic properties of the suspension were measured over a broad range of frequency by a numerical solution that accounted for fluid inertia. Variation of shear amplitude and cell volume percent, and comparison of buffered saline, plasma, and dextran as suspending media showed that the cellular elements had undergone small bending and shearing deformations. Studies of normal adult erythrocytes, hypotonically swollen cells, temperature-altered cells, and erythrocyte ghosts suggested that the method was evaluating membrane material properties. The normal membrane was found to exhibit a shear rate dependent elastic modulus that increased by more than a factor of 20 over a frequency range from 0.0076 Hz to 60 Hz. The membrane viscosity showed a substantial drop with frequency indicative of a frequency thinning phenomenon. At high frequency of deformation the viscous response of normal erythrocytes was no longer indicative of a membrane property due to the dominant influence of the internal hemoglobin solution. The studies generally supported the ability of the method to quantify relative membrane material properties and detect changes in membrane structure. 相似文献
4.
Cortinarius sarcoflammeus is proposed as a new species belonging to subgenus Dermocybe, on the basis of its morphological, chemical and ecological characters. The strong red-orange colour of the context and stipe
base, large spores, sphagnicolous habitat and high dermorubin content are characteristic for the new species. Holotypes of
C. huronensis and C. huronensis var. olivaceus have been examined for comparison, and their differences discussed. Photographs and line drawings of C. sarcoflammeus are added.
Received February 13, 2001 Accepted March 23, 2001 相似文献
5.
6.
7.
8.
Plasma hormones in pre- and postmenopausal breast cancer 总被引:1,自引:0,他引:1
9.
Edmund H. Frank Boyce W. Burge Boleslaw H. Liwnicz Linda J. Lotspeich Jocelyn C. White Steven L. Wechsler Frank H. Mayfield Jeffrey T. Keller 《Experimental cell research》1983,146(2):371-376
Cells from cranial and spinal arachnoid membranes of humans were grown in culture. Their growth characteristics, morphology and details of their cytoskeletal composition are described. Arachnoid membranes, obtained at autopsy, were finely minced and incubated in tissue culture medium. Monolayers of cells of homogeneous morphology grew from these tissue fragments. The cells were flat and polygonal. They divided slowly to form non-overlapping monolayers of low cell density. Electron microscopic examination of cultured arachnoid cells revealed numerous desmosome-like tight junctions and abundant intermediate filaments (tonofilaments). Both morphological features are characteristic of arachnoid cells in situ, but not of cells in the fibroblast-rich dura mater. Immunofluorescence microscopy with monoclonal antibodies demonstrated cytokeratin in the cytoplasm of primary cultures of arachnoid cells. Thus we demonstrated that these cultured cells retained certain of the specific differentiated properties of arachnoid cells in situ and that they are not fibroblasts (which lack tight junctions and cytokeratins). To our knowledge, there have been no previous reports of in vitro growth of arachnoid cells. This in vitro model should be useful in studying the response of arachnoid cells to a variety of substances thought to be involved in the chronic inflammatory condition of the meninges known as arachnoiditis. 相似文献
10.
Anu Lipsanen Stefanie Flunkert Kristina Kuptsova Mikko Hiltunen Manfred Windisch Birgit Hutter-Paier Jukka Jolkkonen 《PloS one》2013,8(3)
Experimental studies have identified a complex link between neurodegeneration, β-amyloid (Aβ) and calcium homeostasis. Here we asked whether early phase β-amyloid pathology in transgenic hAPPSL mice exaggerates the ischemic lesion and remote secondary pathology in the thalamus, and whether a non-selective calcium channel blocker reduces these pathologies. Transgenic hAPPSL (n = 33) and non-transgenic (n = 30) male mice (4–5 months) were subjected to unilateral cortical photothrombosis and treated with the non-selective calcium channel blocker bepridil (50 mg/kg, p.o., once a day) or vehicle for 28 days, starting administration 2 days after the operation. Animals were then perfused for histological analysis of infarct size, Aβ and calcium accumulation in the thalamus. Cortical photothrombosis resulted in a small infarct, which was associated with atypical Aβ and calcium accumulation in the ipsilateral thalamus. Transgenic mice had significantly smaller infarct volumes than non-transgenic littermates (P<0.05) and ischemia-induced rodent Aβ accumulation in the thalamus was lower in transgenic mice compared to non-transgenic mice (P<0.01). Bepridil decreased calcium load in the thalamus (P<0.01). The present data suggest less pronounced primary and secondary pathology in hAPPSL transgenic mice after ischemic cortical injury. Bepridil particularly decreased calcium pathology in the thalamus following ischemia. 相似文献