全文获取类型
收费全文 | 53810篇 |
免费 | 3882篇 |
国内免费 | 2803篇 |
出版年
2024年 | 111篇 |
2023年 | 925篇 |
2022年 | 1285篇 |
2021年 | 1831篇 |
2020年 | 1781篇 |
2019年 | 2441篇 |
2018年 | 2112篇 |
2017年 | 1391篇 |
2016年 | 1545篇 |
2015年 | 1922篇 |
2014年 | 2938篇 |
2013年 | 3955篇 |
2012年 | 2085篇 |
2011年 | 2730篇 |
2010年 | 2046篇 |
2009年 | 2346篇 |
2008年 | 2410篇 |
2007年 | 2548篇 |
2006年 | 2245篇 |
2005年 | 2106篇 |
2004年 | 1854篇 |
2003年 | 1585篇 |
2002年 | 1605篇 |
2001年 | 1388篇 |
2000年 | 1121篇 |
1999年 | 990篇 |
1998年 | 961篇 |
1997年 | 912篇 |
1996年 | 840篇 |
1995年 | 797篇 |
1994年 | 737篇 |
1993年 | 659篇 |
1992年 | 635篇 |
1991年 | 594篇 |
1990年 | 470篇 |
1989年 | 462篇 |
1988年 | 405篇 |
1987年 | 350篇 |
1986年 | 302篇 |
1985年 | 394篇 |
1984年 | 494篇 |
1983年 | 295篇 |
1982年 | 381篇 |
1981年 | 344篇 |
1980年 | 256篇 |
1979年 | 252篇 |
1978年 | 183篇 |
1977年 | 136篇 |
1976年 | 134篇 |
1973年 | 56篇 |
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
91.
Because the acrosome of human sperm is too small to be directly visualized by phase-contrast microscopy, acrosome reactions (that is loss of the acrosome) are generally not evaluated in studies of human sperm capacitation and fertilization. Nevertheless, it would be useful in such studies to have a technique for easily identifying and quantitating acrosome-reacted sperm. In this paper, we describe a method for labeling the human sperm acrosome with fluorescein-conjugated Ricinus communis agglutinin-60 (FITC-RCA); we show that in sperm without acrosomal caps, FITC-RCA labeling occurs either not at all or only in the equatorial segment of the acrosome. To determine if the absence of FITC-RCA labeling in the acrosomal cap region gives a reliable estimate of acrosome reactions, washed sperm or sperm incubated in a capacitating medium (BWW) were divided into two groups, which were then fixed for FITC-RCA labeling or transmission electron microscopy. Counts of acrosome reactions made by each method were similar, and we observed an increase in the percentage of reactions following incubation in BWW. We conclude that the FITC-TCA labeling technique is a reliable method for accurately scoring the percentage of acrosome-reacted human sperm. 相似文献
92.
Fabián Michelangeli Dalia M. Sulcas Marie-Christine Ruiz 《Cell and tissue research》1987,250(2):413-419
Summary This study is concerned with electron-microscopic observations on endocrine or paracrine cells in the fundic gastric mucosa of the bullfrog. Also, an attempt was made to identify the histamine-releasing cells involved in the secretagogue response. At least three distinct endocrine-like cell types were found. The classification is based on the appearance of secretory granules and other organelles, and the relationship of endocrine-like cells with other cells in the tissue. The amphibian endocrine-like cells resemble the ECL, D and EC cells of mammals. Type-I (ECL) cells showed degranulation after repeated stimulation with tetragastrin (TG), acetylcholine (ACh) and K+ depolarizing solution, all of which release histamine. 相似文献
93.
《FEBS letters》1988,240(1-2):88-94
Four subtypes of muscarinic acetylcholine receptor (mAChR) were stably expressed in neuroblastoma-glioma hybrid cells (NG108-15). By combining fluorescent indicator dye (fura-2) studies with electrophysiological measurements it is shown that stimulation of mAChR I and mAChR III readily leads to release of calcium from intracellular stores and to associated conductance changes, whereas stimulation of mAChR II and mAChR IV exerts no such effect. Dose-response curves describing the amplitude or the delay of the calcium rise induced by acetylcholine suggest that the apparent affinity of mAChR III for its agonist is higher by about one order of magnitude than that of mAChR I. Ionic substitution experiments and current fluctuation analysis indicate that calcium activates a K+-specific conductance of ‘small’ single-channel amplitude similar to the SK type [1]. Furthermore, an outward current (M current) suppressed by activation of mAChR I and mAChR III has a single-channel amplitude corresponding to a conductance of approximately 3 pS. 相似文献
94.
Caroline van Haaften-Day Peter Russell Susan Carr Lesley Wright 《In vitro cellular & developmental biology. Plant》1988,24(10):965-971
Summary A cell line derived from a human ovarian carcinosarcoma was established in tissue culture and in nude mice. Two sublines,
LDF and HDF, separated by discontinuous density centrifugation were also established from the parent line JoN. The cloning
efficiency of the JoN line was 21%. Morphologic features of adenocarcinoma cells characteristic of the parent JoN cells were
retained in the sublines and clones; all lines showed the same karyotype and DNA content (pseudodiploid and pseudotetraploid).
Keratin, as demonstrated immunohistochemically, was strongly expressed in the parent line JoN and the xenograft tumor, but
not at all in the LDF sublines and only moderately in the HDF sublines. Vimentin, however, was expressed in neither the parent
line JoN nor the xenograft tumor, but was present in both sublines. Transglutaminase and plasminogen activator activity was
high in the parent line JoN. Neither, sublines nor clones showed the same high enzyme activity as the parent line. It is concluded
that this human tumor line JoN is comprised of epithelial cells, capable of multidirectional differentiation. 相似文献
95.
96.
97.
98.
99.
100.
《Molecular cell》2020,77(4):748-760.e9
- Download : Download high-res image (218KB)
- Download : Download full-size image