全文获取类型
收费全文 | 5250篇 |
免费 | 293篇 |
出版年
2023年 | 10篇 |
2022年 | 34篇 |
2021年 | 74篇 |
2020年 | 33篇 |
2019年 | 35篇 |
2018年 | 75篇 |
2017年 | 59篇 |
2016年 | 97篇 |
2015年 | 192篇 |
2014年 | 207篇 |
2013年 | 293篇 |
2012年 | 333篇 |
2011年 | 354篇 |
2010年 | 211篇 |
2009年 | 201篇 |
2008年 | 305篇 |
2007年 | 338篇 |
2006年 | 322篇 |
2005年 | 275篇 |
2004年 | 307篇 |
2003年 | 309篇 |
2002年 | 291篇 |
2001年 | 79篇 |
2000年 | 75篇 |
1999年 | 90篇 |
1998年 | 65篇 |
1997年 | 59篇 |
1996年 | 42篇 |
1995年 | 48篇 |
1994年 | 38篇 |
1993年 | 31篇 |
1992年 | 62篇 |
1991年 | 51篇 |
1990年 | 69篇 |
1989年 | 53篇 |
1988年 | 49篇 |
1987年 | 46篇 |
1986年 | 35篇 |
1985年 | 40篇 |
1984年 | 28篇 |
1983年 | 30篇 |
1982年 | 26篇 |
1981年 | 19篇 |
1980年 | 17篇 |
1979年 | 14篇 |
1978年 | 12篇 |
1977年 | 17篇 |
1976年 | 14篇 |
1975年 | 17篇 |
1974年 | 12篇 |
排序方式: 共有5543条查询结果,搜索用时 30 毫秒
1.
Hironori Hirata 《Bulletin of mathematical biology》1982,44(5):697-704
This paper has studied the evolution of a predator-prey Volterra-Lotka ecosystem with saturation effect for the general case
where both predator and prey evolve. We have interesting results under the evolutional condition, as follows: (1) the predator
population and the ratio of predator to prey populations increase; (2) the parameters of the prey drift in the direction of
increasing multiplication rate and saturation level, while the parameters of the predator drift in the direction of decreasing
death rate. 相似文献
2.
A new snake-eel,Apterichtus keramanus, is described on the basis of a single 276-mm TL specimen trawled from the coast of Kerama Islands, Okinawa Prefecture, Japan.
The species is unique in the genus in having the posterior nostril opening entirely inside the mouth and a dark band running
from the anteroventral margin of the eye to the upper lip. 相似文献
3.
Takahiro Ishii Tatsufumi Okino Yosuke Mino Hiroaki Tamiya Fuyuhiko Matsuda 《Plant Growth Regulation》2007,52(2):131-139
Starfish waste has been shown to be an effective compost material not only in the promotion of plant growth but also in terms
of having insecticidal activity. In the present study, plant growth regulation by chemicals from starfish was examined. The
aqueous fraction from a hot water extract of the starfish Asterias amurensis Lütken showed plant-growth activity, while the aqueous fraction from a methanol extract inhibited growth of Brassica campestris. The lipophilic fraction from the methanol extract also exhibited a plant growth-promoting effect. The active components
from each extract were identified. Asterubine from the hot water extract promoted plant growth. A ceramide from the lipophilic
fraction showed root growth promoting effect, and three glucocerebrosides had promotive effects on the entire plant. Asterosaponins
were identified as the main growth inhibitors in the aqueous fraction of the methanol extract. These active compounds from
starfish waste could be analyzed as potential plant growth regulators in agricultural applications in the future. 相似文献
4.
Human and nonhuman primates comprehend the actions of other individuals by detecting social cues, including others’ goal-directed motor actions and faces. However, little is known about how this information is integrated with action understanding. Here, we present the ontogenetic and evolutionary foundations of this capacity by comparing face-scanning patterns of chimpanzees and humans as they viewed goal-directed human actions within contexts that differ in whether or not the predicted goal is achieved. Human adults and children attend to the actor’s face during action sequences, and this tendency is particularly pronounced in adults when observing that the predicted goal is not achieved. Chimpanzees rarely attend to the actor’s face during the goal-directed action, regardless of whether the predicted action goal is achieved or not. These results suggest that in humans, but not chimpanzees, attention to actor’s faces conveying referential information toward the target object indicates the process of observers making inferences about the intentionality of an action. Furthermore, this remarkable predisposition to observe others’ actions by integrating the prediction of action goals and the actor’s intention is developmentally acquired. 相似文献
5.
Daisuke Hirata Alexei V. Abramov Gennady F. Baryshnikov Ryuichi Masuda 《Biological journal of the Linnean Society. Linnean Society of London》2014,111(3):627-635
Sequence analyses of the complete brown bear, Ursus arctos, mitochondrial DNA (mtDNA) genome have detected scattered single nucleotide polymorphisms (SNPs) that define distinct mtDNA haplogroups in phylogeographical studies. The degraded DNA in historical samples, such as stuffed or excavated specimens, however, is often not suitable for sequence analyses. To address this problem, we developed an amplified product length polymorphism (APLP) analysis for mtDNA‐haplogrouping U. arctos specimens by detecting haplogroup‐specific SNPs. We verified the validity and utility of this method by analysing up to 170‐year‐old skin samples from U. arctos specimens collected widely across continental Eurasia. We detected some of the same haplogroups as those occurring in eastern Hokkaido (Japan) and eastern Alaska in continental Eurasia (the Altai and the Caucasus). Our results show that U. arctos in eastern Hokkaido and eastern Alaska descended from a common ancestor in continental Eurasia, and suggest that U. arctos occupied several refugia in southern Asia during the Last Glacial Maximum. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 111 , 627–635. 相似文献
6.
Modulation of brain progestin and glucocorticoid receptors by unsaturated fatty acid and phospholipid 总被引:1,自引:0,他引:1
J Kato A Takano N Mitsuhashi N Koike K Yoshida S Hirata 《Journal of steroid biochemistry》1987,27(4-6):641-648
In an attempt to learn how nonsteroidal factors modulate brain progestin and glucocorticoid receptors, the effects of saturated and unsaturated fatty acids, and phosphatidylinositol on the binding of [3H]R5020 or [3H]dexamethasone, determined by sucrose density gradient and gel filtration on LH20, were examined in the cerebral cortical cytosol from 10-day-old female rats which contain a considerable amount of progestin and glucocorticoid receptors. Unsaturated fatty acids such as oleic (C18:1), arachidonic (C20:4) and docosahexaenoic acid (C22:4) depressed the [3H]R5020 or [3H]dexamethasone binding in increasing order, but saturated fatty acids had no effect. Arachidonic and docosahexaenoic acids, which were strong inhibitors, lowered the binding dose dependently. The fatty acid inhibition on brain progestin and glucocorticoid receptors was thus a function of acid dose and degree of acid unsaturation. Interestingly, prostaglandin D2 did not show any effect. Among phospholipids tested the inhibitory effect of phosphatidylinositol on the [3H]R5020 binding was evident, but no significant effect was found with phosphatidylethanolamine, phosphatidylcholine, phosphatidylserine or sphingomyelin. The phosphatidylinositol inhibition was dose dependent. Analysis on kinetics and Scatchard plot have revealed the noncompetitive type of inhibition by arachidonic acid and phosphatidylinositol. From these results it is suggested that the unsaturated nonestrified fatty acid, arachidonic acid, and phosphoinositides modulate the brain progestin and, possibly, glucocorticoid receptors through their binding at sites different from steroid binding sites on the respective receptor molecules. 相似文献
7.
Structure and expression of cDNA for an inhibitor of blood coagulation isolated from human placenta: a new lipocortin-like protein 总被引:10,自引:0,他引:10
A Iwasaki M Suda H Nakao T Nagoya Y Saino K Arai T Mizoguchi F Sato H Yoshizaki M Hirata 《Journal of biochemistry》1987,102(5):1261-1273
An inhibitor of blood coagulation, a new protein with an apparent molecular weight of 34,000 and an isoelectric point of 4.9, was purified from human placental tissue by EDTA extraction. Five cDNA clones were isolated from the human placental lambda gt11 cDNA library using the mouse monoclonal antibody raised against the coagulation inhibitor as the probe. The longest insert consists of 1,566 nucleotides, and contains 960 nucleotides entirely encoding the 320 amino acids of the inhibitor, and a poly A tail. The deduced amino acid sequence was corroborated by chemical analyses of the protein. The entire amino acid sequence shows homology to those of lipocortin I, lipocortin II, and endonexin-related proteins. The cDNA for the inhibitor was expressed in Escherichia coli under the regulation of the trc promotor of the plasmid pKK233-2. The resulting recombinant protein manifested inhibitory activities against both blood coagulation and phospholipase A2 activity, as did the coagulation inhibitor isolated from human placenta. 相似文献
8.
Effects of calcium-antagonists and calmodulin inhibitors on DNA synthesis in cultured rat vascular smooth muscle cells 总被引:1,自引:0,他引:1
To investigate the role of intracellular Ca2+ in the mechanism of cellular proliferation of vascular smooth muscle cells (VSMC), the effects of Ca2+-antagonists and calmodulin (CaM) inhibitors on DNA synthesis stimulated by serum-derived growth factors were studied in cultured VSMCs derived from rat aorta. DNA synthesis assessed by incorporation of [3H]thymidine into the cells was significantly stimulated by epidermal growth factor (EGF), platelet-derived growth factor (PDGF) or fetal bovine serum (FBS), of which the effects were dose-dependently inhibited by a variety of Ca2+-antagonists, such as verapamil, diltiazem and nicardipine. Trifluoperazine and W-7, both specific CaM inhibitors, similarly inhibited DNA synthesis stimulated by EGF, PDGF or FBS in a dose-dependent manner, whereas W-5, a less specific CaM inhibitor, was minimally effective. These data suggest that the Ca2+-CaM system plays an important role in the mechanism of growth factor-induced DNA synthesis in VSMCs. 相似文献
9.
Mikihiko Naito Ichiro Kudo Yukiko Mukai-Sato Susumu Tsushima Hiroaki Nomura Shoshichi Nojima Keizo Inoue 《Cancer immunology, immunotherapy : CII》1987,24(2):158-164
Summary Liposomes composed of chemically synthesized glyceroglycolipids, such as 1,2-dipalmityl-[-cellobiosyl-(1 3)]-glycerol (Cel-DAG), 1,2-dipalmityl-[-lactosyl-(1 3)]-glycerol, or 1,2-dipalmityl-[-maltosyl-(1 3)]-glycerol, were found to enhance protective immunity against transplantable tumor cells (sarcoma 180) in ICR mice. Peritoneal exudate cells prepared from mice treated in vivo with Cel-DAG showed cytostatic activity in vitro against the mouse leukemia cell line, EL-4. Adherent cells separated from this preparation showed similar activity. Peritoneal cells from polypeptone-injected mice acquired appreciable cytostatic activity when incubated in vitro in the presence of glyceroglycolipid liposomes. The adherent cell fraction alone showed rather weak cytostatic activity when pretreated with the glyceroglycolipids, and full activity was restored by supplementing with the nonadherent cell fraction. The ability of glycolipids to induce tumoricidal effects was affected by cholesterol content: with increasing cholesterol content, the activities decreased. Cholesterol-free glycolipid liposomes were taken more efficiently by macrophages than cholesterol-containing liposomes. Cholersterol modifies the surface property of glyceroglycolipid liposomes. Activation of macrophages is responsible for enhancement of protective immunity against tumor cells by injection of these glycolipids in vivo.This work was supported in part by Grants-in-Aid (Nos. 58010010, and 59870076) for Scientific Research from the Ministry of Education, Science and Culture of Japan 相似文献
10.
Interleukin-6 triggers the association of its receptor with a possible signal transducer, gp130 总被引:109,自引:0,他引:109
T Taga M Hibi Y Hirata K Yamasaki K Yasukawa T Matsuda T Hirano T Kishimoto 《Cell》1989,58(3):573-581
Interleukin-6 mediates pleiotropic functions in various types of cells through its specific receptor (IL-6-R), the cDNA of which has already been cloned. We report here that an 80 kd single polypeptide chain (IL-6-R) is involved in IL-6 binding and that IL-6 triggers the association of this receptor with a non-ligand-binding membrane glycoprotein, gp130. The association takes place at 37 degrees C within 5 min and is stable for at least 40 min in the presence of IL-6, but does not occur at 0 degree C. Human IL-6-R can associate with a murine gp130 homolog and is functional in murine cells. Mutant IL-6-R lacking the intracytoplasmic portion is functional, suggesting that the two polypeptide chains interact to involve their extracellular portion. In fact, a soluble IL-6-R lacking the transmembrane and intracytoplasmic domains can associate with gp130 in the presence of IL-6 and mediate its function. These findings indicate that the complex of IL-6 and IL-6-R can interact with a non-ligand-binding membrane glycoprotein, gp130, extracellularly and can provide the IL-6 signal. 相似文献