全文获取类型
收费全文 | 1529篇 |
免费 | 252篇 |
国内免费 | 1篇 |
出版年
2021年 | 19篇 |
2018年 | 22篇 |
2016年 | 21篇 |
2015年 | 38篇 |
2014年 | 34篇 |
2013年 | 57篇 |
2012年 | 58篇 |
2011年 | 66篇 |
2010年 | 53篇 |
2009年 | 45篇 |
2008年 | 65篇 |
2007年 | 54篇 |
2006年 | 44篇 |
2005年 | 58篇 |
2004年 | 57篇 |
2003年 | 58篇 |
2002年 | 48篇 |
2001年 | 48篇 |
2000年 | 57篇 |
1999年 | 37篇 |
1998年 | 19篇 |
1997年 | 20篇 |
1996年 | 25篇 |
1995年 | 24篇 |
1994年 | 18篇 |
1993年 | 24篇 |
1992年 | 33篇 |
1991年 | 59篇 |
1990年 | 37篇 |
1989年 | 29篇 |
1988年 | 30篇 |
1987年 | 31篇 |
1986年 | 27篇 |
1985年 | 20篇 |
1984年 | 23篇 |
1983年 | 23篇 |
1982年 | 17篇 |
1981年 | 23篇 |
1979年 | 26篇 |
1978年 | 21篇 |
1977年 | 18篇 |
1975年 | 17篇 |
1974年 | 16篇 |
1973年 | 15篇 |
1972年 | 18篇 |
1971年 | 16篇 |
1970年 | 20篇 |
1969年 | 15篇 |
1967年 | 20篇 |
1966年 | 16篇 |
排序方式: 共有1782条查询结果,搜索用时 31 毫秒
21.
Effect of Restricted Root Growth on Carbohydrate Metabolism and Whole Plant Growth of Cucumis sativus L 总被引:9,自引:3,他引:6
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)
The effects of varied rooting volumes on root growth and source leaf carbohydrate metabolism were studied in greenhouse-grown cucumber (Cucumis sativus L cv Calypso) plants. Plants were grown for 7 weeks in container volumes that ranged from 0.4 to 5.9 liters. Plants grown in the smaller containers exhibited less leaf expansion, lower root and shoot weight, and fewer lateral stems than plants grown in the 5.9 liter containers. Shoot/root ratio was not altered by the container volume, suggesting coordination of root and shoot growth due to rooting volume. Source leaf carbon exchange rates, assimilate export rates, and starch accumulation rates for plants grown in 0.4 liter containers were approximately one-half or less in comparison to those for plants grown in 5.9 liter containers. Starch concentrations per unit leaf area were maintained at high levels in source leaves of plants grown in 0.4 liter containers over the entire day/night cycle. Lower extractable galactinol synthase activities and higher galactinol concentrations occurred in leaves of plants grown in 0.4 liter container volumes. The reduced sink demand, induced by restricted root growth, may have led to increased starch concentrations and to a reduction in stachyose biosynthesis in cucumber source leaves. 相似文献
22.
The nucleoplasmin nuclear location sequence is larger and more complex than that of SV-40 large T antigen 总被引:36,自引:11,他引:25
下载免费PDF全文
![点击此处可从《The Journal of cell biology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
C Dingwall J Robbins S M Dilworth B Roberts W D Richardson 《The Journal of cell biology》1988,107(3):841-849
The carboxy-terminal tail of nucleoplasmin, which specifies entry into the cell nucleus, contains four short sequences that are similar to previously identified nuclear location sequences. We show that none of these is able to locate chicken muscle pyruvate kinase to the cell nucleus. Deletion analysis was used to determine the limits of a nuclear location sequence and indicated that a 14-amino acid segment (RPAATKKAGQAKKK) should function as a minimal nuclear location sequence. When tested directly, however, this sequence was unable to locate pyruvate kinase to the cell nucleus. Restoration of three amino acids of nucleoplasmin sequence at either end of this sequence generated sequences that were able to locate pyruvate kinase to the cell nucleus. The 14-amino acid proposed minimal nuclear location sequence is present in the functional sequences, AVKRPAATKKAGQAKKK, RPAATKKAGQAKKKKLD, and the sequence AVKRPAATKKAGQAKKKKLD, which has additional amino acids at both ends. The minimal sequence element is therefore necessary but not sufficient for transport into the cell nucleus. This unusual feature of the nucleoplasmin nuclear location sequence suggests ways in which it could interact with the nuclear transport mechanism. 相似文献
23.
Structure-function analysis of hepatocyte growth factor: identification of variants that lack mitogenic activity yet retain high affinity receptor binding. 总被引:11,自引:0,他引:11
下载免费PDF全文
![点击此处可从《The EMBO journal》网站下载免费的PDF全文](/ch/ext_images/free.gif)
N A Lokker M R Mark E A Luis G L Bennett K A Robbins J B Baker P J Godowski 《The EMBO journal》1992,11(7):2503-2510
Hepatocyte growth factor (HGF) is a potent mitogen for parenchymal liver, epithelial and endothelial cells. Structurally, it has similarities to kringle-containing serine proteases, although it does not possess proteolytic activity. A structure-activity relationship study of human HGF was performed by functional analysis of HGF substitution and deletion variants. Analysis of HGF variants was accomplished by defining their ability to induce DNA synthesis on hepatocytes in primary culture and to compete with wild-type HGF for binding to a soluble form of the HGF receptor. Three groups of variants were made: (i) substitutions at the cleavage site, (ii) substitutions within the protease-like domain and (iii) deletions of the beta-chain and/or kringle domains. Our results show that: (i) single-chain HGF is a zymogen-like promitogen in that cleavage into a two-chain form is required for biological activity, however, the single chain form of HGF still retains substantial receptor binding capacity; (ii) certain mutations in the protease-like domain result in variants that are completely defective for mitogenic activity, yet exhibit apparent receptor binding affinities similar to wild-type HGF (Kd approximately 50-70 pM); and (iii) a variant containing the N-terminal 272 residues of mature HGF showed only a 4-fold increase in Kd when compared with wild-type HGF indicating that a primary receptor binding determinant is located within this sequence. 相似文献
24.
Effect of brefeldin A on alphaherpesvirus membrane protein glycosylation and virus egress. 总被引:30,自引:28,他引:2
下载免费PDF全文
![点击此处可从《Journal of virology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
In this work we used brefeldin A (BFA), a specific inhibitor of export to the Golgi apparatus, to study pseudorabies virus viral glycoprotein processing and virus egress. BFA had little effect on initial synthesis and cotranslational modification of viral glycoproteins in the endoplasmic reticulum (ER), but it disrupted subsequent glycoprotein maturation and export. Additionally, single-step growth experiments demonstrated that after the addition of BFA, accumulation of infectious virus stopped abruptly. BFA interruption of virus egress was reversible. Electron microscopic analysis of infected cells demonstrated BFA-induced disappearance of the Golgi apparatus accompanied by a dramatic accumulation of enveloped virions between the inner and outer nuclear membranes and also in the ER. Large numbers of envelope-free capsids were also present in the cytoplasm of all samples. In control samples, these capsids were preferentially associated with the forming face of Golgi bodies and acquired a membrane envelope derived from the trans-cisternae. Our results are consistent with a multistep pathway for envelopment of pseudorabies virus that involves initial acquisition of a membrane by budding of capsids through the inner leaf of the nuclear envelope followed by deenvelopment and release of these capsids from the ER into the cytoplasm in proximity to the trans-Golgi. The released capsids then acquire a bilaminar double envelope containing mature viral glycoproteins at the trans-Golgi. The resulting double-membraned virus is transported to the plasma membrane, where membrane fusion releases a mature, enveloped virus particle from the cell. 相似文献
25.
26.
T H Robbins 《Plastic and reconstructive surgery》1991,87(3):567-568
A technique is described for reinforcing and sealing a microvascular anastomosis by using a detached vessel segment as a cuff around the anastomosis. This may allow fewer microvascular sutures to be used. This would allow a simpler, less traumatic, and more rapid repair and may allow "more vessels to be repaired by more people." 相似文献
27.
Donna Robbins Colin A. Chapman Richard W. Wrangham 《Primates; journal of primatology》1991,32(3):301-305
Gibbons and spider monkeys have similar diets, body size, and locomotor patterns. They are therefore expected to be subject
to similar socioecological rules. However their grouping patterns differ. Gibbons live in small stable groups, whereas spider
monkey form unstable sub-groups that vary from small to large during different seasons. If similar principles apply to the
two species, food abundance should vary more for spider monkeys than for gibbons; food density should be similar for the two
species when spider monkey sub-groups are the same size as gibbon groups; and the highest level of food abundance should be
higher for spider monkeys than for gibbons. These predictions are upheld for a comparison of particular populations ofHylobates muelleri andAteles geoffroyi. 相似文献
28.
29.
M A Von Tersch H L Robbins C S Jany T B Johnson 《Applied and environmental microbiology》1991,57(2):349-358
Genes encoding insecticidal crystal proteins were cloned from three strains of Bacillus thuringiensis subsp. kenyae and two strains of B. thuringiensis subsp. kurstaki. Characterization of the B. thuringiensis subsp. kenyae toxin genes showed that they are most closely related to cryIA(c) from B. thuringiensis subsp. kurstaki. The cloned genes were introduced into Bacillus host strains, and the spectra of insecticidal activities of each Cry protein were determined for six pest lepidopteran insects. CryIA(c) proteins from B. thuringiensis subsp. kenyae are as active as CryIA(c) proteins from B. thuringiensis subsp. kurstaki against Trichoplusia ni, Lymantria dispar, Heliothis zea, and H. virescens but are significantly less active against Plutella xylostella and, in some cases, Ostrinia nubilalis. The sequence of a cryIA(c) gene from B. thuringiensis subsp. kenyae was determined (GenBank M35524) and compared with that of cryIA(c) from B. thuringiensis subsp. kurstaki. The two genes are more than 99% identical and show seven amino acid differences among the predicted sequences of 1,177 amino acids. 相似文献
30.
Induction by ionizing radiation of the gadd45 gene in cultured human cells: lack of mediation by protein kinase C. 总被引:18,自引:2,他引:16
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)
M A Papathanasiou N C Kerr J H Robbins O W McBride I Alamo Jr S F Barrett I D Hickson A J Fornace Jr 《Molecular and cellular biology》1991,11(2):1009-1016
The effect of ionizing radiation on the expression of two DNA-damage-inducible genes, designated gadd45 and gadd153, was examined in cultured human cells. These genes have previously been shown to be strongly and coordinately induced by UV radiation and alkylating agents in human and hamster cells. We found that the gadd45 but not the gadd153 gene is strongly induced by X rays in human cells. The level of gadd45 mRNA increased rapidly after X rays at doses as low as 2 Gy. After 20 Gy of X rays, gadd45 induction, as measured by increased amounts of mRNA, was similar to that produced by the most effective dose of the alkylating agent methyl methanesulfonate. No induction was seen after treatment of either human or hamster cells with 12-O-tetradecanoylphorbol-13-acetate, a known activator of protein kinase C (PKC). Therefore, gadd45 represents the only known mammalian X-ray-responsive gene whose induction is not mediated by PKC. However, induction was blocked by the protein kinase inhibitor H7, indicating that induction is mediated by some other kinase(s). Sequence analysis of human and hamster cDNA clones demonstrated that this gene has been highly conserved and encodes a novel 165-amino-acid polypeptide which is 96% identical in the two species. This gene was localized to the short arm of human chromosome 1 between p12 and p34. When induction in lymphoblast lines from four normal individuals was compared with that in lines from four patients with ataxia telangiectasia, induction by X rays of gadd45 mRNA was less in the cell lines from this cancer-prone radiosensitive disorder. Our results provide evidence for the existence of an X-ray stress response in human cells which is independent of PKC and which is abnormal in taxia telangiectasia. 相似文献