全文获取类型
收费全文 | 747623篇 |
免费 | 88626篇 |
国内免费 | 348篇 |
专业分类
836597篇 |
出版年
2018年 | 6454篇 |
2016年 | 8632篇 |
2015年 | 11843篇 |
2014年 | 13739篇 |
2013年 | 20244篇 |
2012年 | 22447篇 |
2011年 | 22893篇 |
2010年 | 15351篇 |
2009年 | 14323篇 |
2008年 | 20452篇 |
2007年 | 20935篇 |
2006年 | 19743篇 |
2005年 | 18844篇 |
2004年 | 18445篇 |
2003年 | 18080篇 |
2002年 | 17521篇 |
2001年 | 33599篇 |
2000年 | 34018篇 |
1999年 | 27265篇 |
1998年 | 9772篇 |
1997年 | 10450篇 |
1996年 | 9981篇 |
1995年 | 9204篇 |
1994年 | 9219篇 |
1993年 | 9258篇 |
1992年 | 23205篇 |
1991年 | 22604篇 |
1990年 | 22043篇 |
1989年 | 21783篇 |
1988年 | 19991篇 |
1987年 | 19181篇 |
1986年 | 17938篇 |
1985年 | 17911篇 |
1984年 | 14860篇 |
1983年 | 12984篇 |
1982年 | 9966篇 |
1981年 | 8833篇 |
1980年 | 8571篇 |
1979年 | 14301篇 |
1978年 | 11239篇 |
1977年 | 10171篇 |
1976年 | 9683篇 |
1975年 | 10593篇 |
1974年 | 10997篇 |
1973年 | 10908篇 |
1972年 | 9911篇 |
1971年 | 8962篇 |
1970年 | 7702篇 |
1969年 | 7327篇 |
1968年 | 6615篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Phytochrome A regulates red-light induction of phototropic enhancement in Arabidopsis. 总被引:20,自引:5,他引:15
下载免费PDF全文
![点击此处可从《Plant physiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Phytochrome A (phyA) and phytochrome B photoreceptors have distinct roles in the regulation of plant growth and development. Studies using specific photomorphogenic mutants and transgenic plants overexpressing phytochrome have supported an evolving picture in which phyA and phytochrome B are responsive to continuous far-red and red light, respectively. Photomorphogenic mutants of Arabidopsis thaliana that had been selected for their inability to respond to continuous irradiance conditions were tested for their ability to carry out red-light-induced enhancement of phototropism, which is an inductive phytochrome response. We conclude that phyA is the primary photoreceptor regulating this response and provide evidence suggesting that a common regulatory domain in the phyA polypeptide functions for both high-irradiance and inductive phytochrome responses. 相似文献
992.
993.
994.
K. Sasikala Ch.V. Ramana P. Raghuveer Rao M. Subrahmanyam 《FEMS microbiology letters》1990,72(1-2):23-28
Abstract Photoproduction of hydrogen, nitrogenase activity (acetylene reduction) and hydrogenase activity (methylene blue dye reduction) were studied in free and alginate immobilized whole cells of a purple non-sulfur photosynthetic bacterium Rhodobacter sphaeroides O.U. 001. Four-fold increase in hydrogen production, two-fold increase in nitrogenase activity and 1.2-fold increase in the hydrogenase activity were observed in immobilized cells compared to free cells. Effect of various inhibitors (CO and C2 H2 ) and electron donor (H2 ) on the above three functions by free and immobilized cells has also been studied. 相似文献
995.
Complete amino acid sequence of a novel integrin beta subunit (beta 6) identified in epithelial cells using the polymerase chain reaction 总被引:18,自引:0,他引:18
D Sheppard C Rozzo L Starr V Quaranta D J Erle R Pytela 《The Journal of biological chemistry》1990,265(20):11502-11507
The integrin family of adhesion receptors consists of several heterodimeric glycoproteins, each composed of one alpha and one beta subunit. Three different mammalian beta subunits, beta 1, beta 2, and beta 3, have been sequenced, but recent evidence suggests the existence of several others. Amplification of guinea pig airway epithelial cell cDNA with oligonucleotide primers designed to recognize consensus integrin beta subunit sequences led to the identification of a novel partial cDNA sequence. Clones containing portions of this sequence were used to screen cDNA libraries constructed from the human pancreatic carcinoma cell line FG-2 and identified a series of overlapping clones encoding the full-length sequence of the human homologue of this protein. This sequence of 788 amino acids is 43, 38, and 47% identical to the sequences of beta 1, beta 2, and beta 3, respectively. Features shared between this novel protein and the previously sequenced beta subunits include the positions of all 56 cysteine residues in the extracellular domain, the single putative transmembrane domain, and the short putative cytoplasmic domain. However, a unique 11-amino acid extension at the carboxyl terminus, not present in any of the other beta subunits, is suggestive of distinctive interactions with cytoplasmic components. Comparison of the human and guinea pig sequences reveals a high degree (94%) of cross-species conservation. Because this protein is clearly distinct from the two other recently described integrins beta 4 and beta 5, we propose to designate it beta 6. 相似文献
996.
An assessment was made of two methods for determining the potency of tissue-type plasminogen activator (TPA). A chromogenic microtitre plate assay was established which contained TPA, plasminogen, a synthetic plasmin substrate (H-D-valyl-L-leucyl-L-lysyl-p-nitroaniline dihydrochloride, S2251) and any one of the following stimulators: native fibrinogen, enzymatic and chemical digests of fibrinogen, poly-D-lysine (PDL) and chemical derivatives of the latter. The chromogen assay was compared with an automated clot-lysis (turbidimetric) assay for sensitivity, reproducibility and validity for potency determination. Reference preparations of TPA were titrated in both assays: in the chromogen assay the dose-response curves were non-parallel, whereas parallelism was observed in the clot-lysis assay. Thus, the chromogen assay was restricted in its applicability and disqualified from any routine regulatory use. The potency of individual lots of recombinant (r)TPA could only be estimated in International Units (IU) of TPA activity with the automated clot-lysis assay and the potency values obtained (IU/vial) were in remarkably close agreement with the manufacturers' values. 相似文献
997.
N. G. Gladkovich A. D. Vorob'eva V. S. Lushchekin K. V. Shuleikina 《Neurophysiology》1991,23(4):289-296
Three types of Golgi-stained neurons were discovered in brain stem reticular nuclei of 30-day-old kittens: sparsely branching reticular neurons, those with densely branching dendritic trees, and giant multipolar neurons (Leontovich's classification). Adopting computerized morphometric techniques enabled 23 different parameters to be measured in cells of these types. The measurements taken from the neuronal groups investigated revealed statistically significant differences between them for most parameters. It was concluded from this that each of the neuronal types distinguished has its own morphological identity (or stability). Characteristics of structural differences and properties of differing cell types in reticular nuclei are discussed in relation to their functional properties.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 23, No. 4, pp. 399–409, July–August, 1991. 相似文献
998.
999.
1000.
The cytomegalovirus enhancer: a pan-active control element in transgenic mice. 总被引:41,自引:2,他引:39
下载免费PDF全文
![点击此处可从《Molecular and cellular biology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
In an effort to identify widely active positive regulatory elements, we have examined the action of the cytomegalovirus enhancer-promoter in transgenic mice. These elements activated expression in 24 of 28 tissues tested. The greatest expression was observed in the heart, kidney, brain, and testis. Maximum expression further localized to specific cells within the heart and kidney. 相似文献