全文获取类型
收费全文 | 31812篇 |
免费 | 2413篇 |
国内免费 | 9篇 |
专业分类
34234篇 |
出版年
2024年 | 24篇 |
2023年 | 239篇 |
2022年 | 518篇 |
2021年 | 956篇 |
2020年 | 588篇 |
2019年 | 741篇 |
2018年 | 886篇 |
2017年 | 748篇 |
2016年 | 1269篇 |
2015年 | 1990篇 |
2014年 | 2137篇 |
2013年 | 2553篇 |
2012年 | 3057篇 |
2011年 | 2753篇 |
2010年 | 1730篇 |
2009年 | 1467篇 |
2008年 | 1865篇 |
2007年 | 1825篇 |
2006年 | 1670篇 |
2005年 | 1448篇 |
2004年 | 1382篇 |
2003年 | 1153篇 |
2002年 | 1048篇 |
2001年 | 196篇 |
2000年 | 154篇 |
1999年 | 205篇 |
1998年 | 208篇 |
1997年 | 167篇 |
1996年 | 153篇 |
1995年 | 113篇 |
1994年 | 112篇 |
1993年 | 86篇 |
1992年 | 78篇 |
1991年 | 60篇 |
1990年 | 59篇 |
1989年 | 66篇 |
1988年 | 50篇 |
1987年 | 41篇 |
1986年 | 28篇 |
1985年 | 38篇 |
1984年 | 45篇 |
1983年 | 36篇 |
1982年 | 24篇 |
1981年 | 27篇 |
1980年 | 31篇 |
1979年 | 25篇 |
1978年 | 20篇 |
1977年 | 15篇 |
1976年 | 20篇 |
1974年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
Silver nitrate stains the intercellular junctions of the endothelium and other cytoplasmic or membrane components. Two protocols are described for the silver staining of rat carotid endothelium that exclude the use of pressurized fixatives and simplify the technique previously described for rat aorta. The entire surface of the carotid endothelium was examined and several parameters (stigmata, granularity, clustering of anionic sites, transversal lines, weakening of silver lines and leukocyte adhesion) were evaluated. We studied the pattern of silver staining in two situations: (1) endothelial activation and (2) neurogenic inflammation. Endothelial activation was produced by the intravenous administration of a proinflammatory albumin or polyinosinic acid. Both products cause a marked increase in leukocyte adhesion concomitant with a decrease in argyrophilia and a weakness or loss of silver lines. Neurogenic inflammation, which is mediated by substances released from sensory nerves, was induced by the intravenous administration of substance P or capsaicin. Both stimuli produced an increase in argyrophilia and weakness or loss of silver lines. Substance P caused a clustering of anionic sites, whereas this phenomenon was more discrete with capsaicin. Nearly 80% of all examined rats (controls and inflammatory stimuli treated) showed endothelial membrane disruptions formed by clusters of cells often in the shape of streaks aligned with the long axis of the vessel. The detection of these discontinuities is important, as loss of endothelial integrity is central in the initiation of pathological events. 相似文献
12.
The concept of the blood-aqueous barrier is largely based on the use of horseradish peroxidase (HRP). The present investigation
was designed to check its reliability as a macromolecular tracer, especially with regard to the transport of plasma proteins.
Rabbits were killed 5 min to 24 h after being intravenously injected with HRP. The tracer diffused rapidly, reaching the aqueous
humor of the eye in 3 min or less and was detected at high concentration in the narrow space between the outer epithelial
layer of the ciliary epithelium and the wall of the pervious capillaries in the stroma of the processes. HRP appeared to migrate
from the blood to the posterior chamber, permeating the tight junctions, viz., the anatomical basis of the blood-aqueous barrier.
It was detected at higher concentration at the anterior surface of the iris, at short time intervals; this was interpreted
as penetration of the tracer from the aqueous humor of the anterior chamber. The choroid was also labeled in continuation
with the reaction in the stroma of the pars plana of the ciliary body which, in turn, sometimes reached the iris root. Therefore,
the pervious blood vessels of the choroid could be a source of macromolecules for the iris root. HRP also induced the formation
of lysosomes in the ciliary epithelium. This can hardly be accepted as the way in which plasma proteins are physiologically
transported to the aqueous humor. However, the pathway of HRP migration over short time intervals seems to be in agreement
with previous research indicating that the entrance of serum albumin into the posterior chamber is the first step of its incorporation
into the aqueous humor.
Received: 7 June 1996 / Accepted: 15 January 1997 相似文献
13.
The magnitudes of inter-chromophore interactions in bacterial photosynthetic reaction centers are investigated by measuring absorption and Stark spectra of reaction centers in which monomeric chromophores are modified and in a novel triplet mutant which lacks the special pair. The circular dichroism spectrum of the triple mutant reaction center was also measured. Only small changes in the spectroscopic properties are observed, as has also been found for several types of reaction centers in which the absorption or chemical properties of a chromophore are altered by site-specific mutations. We conclude that the electronic absorption, circular dichroism and Stark features of the special pair and the monomeric chromophores in the reaction center are relatively insensitive to inter-chromophore interactions. 相似文献
14.
J Ignacio Andrés Jesús Alcázar José M Alonso Adolfo Díaz Javier Fernández Pilar Gil Laura Iturrino Encarna Matesanz Theo F Meert Anton Megens Victor K Sipido 《Bioorganic & medicinal chemistry letters》2002,12(2):249-253
Following the programme started at Janssen Research Foundation searching for 5-HT(2A/2C) antagonists, we now report on the synthesis of a series of substituted 2-(Dimethylaminomethyl)-2,3,3a,8-tetrahydrodibenzo[c,f]isoxazolo[2,3-a]azepine derivatives. The 5-HT(2A), 5-HT(2C) and H(1) receptor affinities as well as the mCPP antagonistic activity of the compounds synthesised is described. 相似文献
15.
16.
17.
18.
Purdy LM 《Bioethics》1989,3(1):18-34
The morality of surrogate mothering is analyzed from a "consequentialist" framework which attempts to separate those consequences that invariably accompany a given act from those that accompany it only in particular circumstances. Critics of surrogacy argue that it transfers the burden and risk of pregnancy onto another woman, separates sex and reproduction, and separates reproduction and childrearing; none of these acts is necessarily wrong, either morally or for women's or society's basic interests. While surrogate mothering can be rendered immoral if women are coerced into the practice or become victims of subordinating or penalizing contracts, it has the potential to empower women and increase their status in society by providing a job that is less risky and more enjoyable than other jobs women are forced to take and by achieving greater social recognition for reproductive labor. 相似文献
19.
20.
Cell suspension cultures of the Madagascan Periwinkle Catharanthus roseus (L) G. Don were maintained on Gamborg's B5 medium and their growth monitored by measuring cellular fresh and dry weight, cell number and mitotic activity. Samples of cells of different ages and physiological states were subcultured onto an alkaloid production medium and their rates of growth and alkaloid accumulation measured over a period of 30–45 days. In two experiments the rate of biomass accumulation was directly related to the rate of cellular serpentine accumulation. Possible mechanisms underlying this phenomenon are discussed in relation to the properties of cells comprising the inocula. 相似文献