全文获取类型
收费全文 | 20073篇 |
免费 | 1931篇 |
国内免费 | 2248篇 |
出版年
2024年 | 18篇 |
2023年 | 279篇 |
2022年 | 346篇 |
2021年 | 1081篇 |
2020年 | 802篇 |
2019年 | 983篇 |
2018年 | 808篇 |
2017年 | 661篇 |
2016年 | 912篇 |
2015年 | 1342篇 |
2014年 | 1542篇 |
2013年 | 1607篇 |
2012年 | 1968篇 |
2011年 | 1761篇 |
2010年 | 1111篇 |
2009年 | 1011篇 |
2008年 | 1144篇 |
2007年 | 995篇 |
2006年 | 913篇 |
2005年 | 788篇 |
2004年 | 692篇 |
2003年 | 692篇 |
2002年 | 610篇 |
2001年 | 382篇 |
2000年 | 322篇 |
1999年 | 260篇 |
1998年 | 164篇 |
1997年 | 146篇 |
1996年 | 124篇 |
1995年 | 104篇 |
1994年 | 135篇 |
1993年 | 77篇 |
1992年 | 82篇 |
1991年 | 71篇 |
1990年 | 57篇 |
1989年 | 49篇 |
1988年 | 42篇 |
1987年 | 32篇 |
1986年 | 25篇 |
1985年 | 42篇 |
1984年 | 16篇 |
1983年 | 16篇 |
1982年 | 15篇 |
1981年 | 6篇 |
1980年 | 2篇 |
1979年 | 6篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1973年 | 2篇 |
1971年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
21.
传入C纤维的兴奋在中电针“足三里”激活中缝大核中的作用 总被引:6,自引:0,他引:6
The purpose of the present work is to study whether the analgesia of "Zusanli" EA was mainly produced by its noxious effect. The antidromic C waves on N. peroneus communis innervating the area of "Zusanli" point were recorded. When "Zusanli" point was stimulated by trains of stimuli, the amplitude of the antidromic C wave was obviously decreased due to collision with the orthodromic stimulation. It was suggested that EA of "Zusanli" could excite some C fibers. It was observed that when the stimulation intensity reached the threshold of C fiber, the NRM neurons were obviously activated, and when it reached or exceeded the intensity for producing the maximal C wave, the NRM neurons were highly activated. Therefore, EA analgesia is probably produced mainly by its noxious stimulus component, especially carried by C fibers, via a negative feedback mechanism in modulating pain. 相似文献
22.
23.
龟纹瓢虫成虫的食饵搜索行为——向地域集中型转换的激发和持续时间 总被引:9,自引:1,他引:8
为了研究在15—25lux和230—280lux两种光照条件下雌雄龟纹瓢虫成虫搜索行为转换的因子及作地域集中型搜索持续的时间(giving-up-time——简写为GUT)长短,按Nakamuta(1982)方法给予以下五种刺激:a.和棉蚜接触;b.捕获棉蚜或仅食去撕去量;c.完全吃下捕获的1头棉蚜;d.和琼脂块(2×2×2mm)接触;e.吃下沾有棉蚜体液的琼脂块(2×2×2mm)。以不给予刺激作对照,观察每种刺激对搜索行为转换的激发作用。结果表明五种刺激的任一种刺激都可激发搜索行为的转换。结果还表明GUT值随刺激程度大小而变化,其大小顺序为a=d相似文献
24.
用金桔茎段为外植体,培养在附加1.0毫克/升BA和0.l毫克/升IBA的MS培养基上,诱导愈伤组织和芽形成。观察了愈伤组织和芽形成过程中的组织细胞学变化。培养一周后,在茎组织切口两端开始膨大,细胞增大和开始分裂。培养两周后,开始形成瘤状愈伤组织。在愈伤组织中有形成层状分生组织、维管组织结节和分生细胞团。培养四周后,表层的分生细胞团分化形成大量芽原基,同时愈伤组织深层也出现分生细胞团。带节茎段可从切口两端的愈伤组织分化形成芽,亦可从叶腋的潜伏芽直接形成芽。 相似文献
25.
26.
27.
本文用凝胶直读法、末端鉴定法等相配合,测定了樗蚕(Philosamia cynthia)絲腺5SrRNA的核苷酸顺序:AGACAACGUCCAUACCACGUUGAAAACACCGGUUCUCGUCCGAUCACCGAAGUCAAGCAACGUCGGGCGCGGUCAGUACUUGGAUGGGUGACCGCCUGGGAACACCGCGUGCUGUUGGCUU比较了樗蚕、蓖麻蚕、柞蚕、家蚕、果蝇等5SrRNA结构差异,在分子水平上探讨了昆虫的分化。 相似文献
28.
29.
Expression of c-myc protooncogene in rat lens cells during development,maturation and reversal of galactose cataracts 总被引:2,自引:0,他引:2
Yi Wen Songtao Shu Nalin J. Unakar Isaac Bekhor 《Molecular and cellular biochemistry》1992,112(1):73-79
It is well established that normal patterns of epithelial cell proliferation and metabolism, and of fiber cell differentiation and maturation are essential for the maintenance of transparency in the ocular lens. Several factors, including exposure to high levels of sugars, have been known to result in the compromise of lens transparency. For example, initiation of lens cell damage by galactose induces lens epithelial cells to proliferate. Elevated levels of c-myc mRNA have usually been correlated with rapid cell growth and increased entry of cells into the S phase. Therefore, changes in c-myc mRNA levels may provide an early indication of the stimulation of lens epithelial cells to proliferate and differentiate, which has been postulated to be an early and important event in response to lens cell injury by galactose. By Northern blot hybridization analysis we quantitated c-myc mRNA levels in the lens capsule epithelia of rats (1) exposed to galactose, and (2) undergoing a partial recovery from the galactose-induced cell damage. At the onset of lens cell damage, we find c-myc mRNA to elevate to 6-fold by 24 hr, and by 48 hr decreases to about 3-fold the normal levels. During recovery, c-myc mRNA continues to be expressed at high levels approaching a 10-fold increase by day 12, then decreasing to levels of about 8-fold the control by day 30. The 24 h transitory elevation in c-myc mRNA in lens epithelial cells is in accord with our previous observations on the 24 h increase in MP26, crystallin and aldose reductase mRNAs following a high influx of galactose. Therefore, the elevation in c-myc mRNA as well suggest that galactose appears to cause lens cells to undergo an early transitory period of gene induction following the exposure of lens cells to galactose. 相似文献
30.
Hematopoietic cell phosphatase (Hcph) was identified by amplification of conserved protein tyrosine phosphatase sequences from a myeloid cell line and is predominantly expressed in hematopoietic cells. Hcph is unique in containing two, tandemly repeated, src-homology 2 domains in the amino terminal region of the phosphatase. Using a genomic probe in interspecific backcross analysis, the murine Hcph gene maps to mouse Chromosome 6 and is tightly linked to the Tnfr-2 and Ly-4 genes. 相似文献