全文获取类型
收费全文 | 5017篇 |
免费 | 711篇 |
国内免费 | 1684篇 |
出版年
2024年 | 14篇 |
2023年 | 120篇 |
2022年 | 192篇 |
2021年 | 268篇 |
2020年 | 226篇 |
2019年 | 277篇 |
2018年 | 249篇 |
2017年 | 213篇 |
2016年 | 246篇 |
2015年 | 331篇 |
2014年 | 376篇 |
2013年 | 407篇 |
2012年 | 491篇 |
2011年 | 518篇 |
2010年 | 374篇 |
2009年 | 339篇 |
2008年 | 358篇 |
2007年 | 361篇 |
2006年 | 348篇 |
2005年 | 276篇 |
2004年 | 258篇 |
2003年 | 244篇 |
2002年 | 231篇 |
2001年 | 158篇 |
2000年 | 133篇 |
1999年 | 89篇 |
1998年 | 64篇 |
1997年 | 41篇 |
1996年 | 21篇 |
1995年 | 23篇 |
1994年 | 18篇 |
1993年 | 20篇 |
1992年 | 20篇 |
1991年 | 16篇 |
1990年 | 10篇 |
1989年 | 13篇 |
1988年 | 12篇 |
1987年 | 11篇 |
1986年 | 7篇 |
1985年 | 7篇 |
1984年 | 6篇 |
1983年 | 2篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1962年 | 1篇 |
1950年 | 1篇 |
排序方式: 共有7412条查询结果,搜索用时 46 毫秒
1.
导水管周围灰质(periaqueductal gray,PAG)在疼痛的调控过程中处于一个不可或缺的位置.其不仅是痛觉信息上行传递的重要部位,还是疼痛抑制系统的重要组成部分.在PAG,包括γ-氨基丁酸(γ-aminobutyric acid,GABA)、5-羟色胺(5-hydroxytryptamine,5-HT)和谷氨酸(glutamate,Glu)在内的神经递质以及内源性阿片肽(endogenous opioid peptides,EOP)和内源性大麻素(endocannabinoid,e CB)为代表的神经调质都参与了PAG对疼痛的信息传递以及调节.本文重点综述GABA、5-HT、Glu、EOP和eCB在PAG参与疼痛生理调控机制的研究进展,以期为中枢神经系统的镇痛研究提供一定的理论基础. 相似文献
2.
l-Phenylalanyl-l-Glutamate-Stimulated, Chloride-Dependent Glutamate Binding Represents Glutamate Sequestration Mediated by an Exchange System 总被引:7,自引:6,他引:1
Markus Kessler Gene Petersen Hai Minh Vu Michel Baudry Gary Lynch 《Journal of neurochemistry》1987,48(4):1191-1200
Stimulation of glutamate binding by the dipeptide L-phenylalanyl-L-glutamate (Phe-Glu) was inhibited by the peptidase inhibitor bestatin, suggesting that the stimulation was caused by glutamate liberated from the dipeptide and not by the dipeptide itself. It further suggests that this form of glutamate binding should be reinterpreted as glutamate sequestration and that stimulation of binding both by dipeptides and after preincubation with high concentrations of glutamate is likely to be due to counterflow accumulation. Several other criteria indicate that most of glutamate binding stimulated by chloride represents glutamate sequestration: Binding is reduced when the osmolarity of the incubation medium is increased, when membranes incubated with [3H]glutamate are lysed before filtration, and when membranes are made permeable by transient exposure to saponin. Moreover, dissociation of bound glutamate after a 100-fold dilution of the incubation medium is accelerated about 50 times by the addition of glutamate to the dilution medium. This result would be anomalous if glutamate were bound to a receptor site; it suggests instead that glutamate is transported in and out of membrane vesicles by a transport system that preferentially mediates exchange between internal and external glutamate. Glutamate binding contains a component of glutamate sequestration even when measured in the absence of chloride. Sequestration is adequately abolished only after treating membranes with detergents; even extensive lysis, sonication, and freezing/thawing may be insufficient. 相似文献
3.
中国黑缘蝽属新种记述(半翅目:缘蝽科) 总被引:4,自引:0,他引:4
中国黑缘蝽属(Hygia Uhler)为缘蝽科缘蝽亚科中较大的属,体均为黑色,常具黄色或褐黄色斑。截止到目前已记载19种,现由近年来采集的标本中又发现7新种,分属于两个亚属:黑缘蝽亚属Hygia Uhler及沟缘蝽亚属Colpura Bergroth,现描述如下。文内所用量度单位均为毫米。模式标本除注明者外,均存放南开大学生物系。 相似文献
4.
Seasonal plasticity in growth and development of the speckled wood butterfly, Pararge aegeria (Satyrinae) 总被引:2,自引:0,他引:2
SÖREN NYLIN PER-OLOF WICKMAN CHRISTER WIKLUND 《Biological journal of the Linnean Society. Linnean Society of London》1989,38(2):155-171
Regulation of growth and development by photoperiod was studied in a population of the speckled wood butterfly, Purarge aegeria L. (Lepidoptera: Satyrinae), from southern Sweden. Individuals were reared in a range of photoperiodic regimes (9L. to 22L) and temperatures (13°C to 21° C). Plasticity was found for important life-history traits- generation time, growth rate and final weight and seasonal regulation of development in response to photoperiod was found to occur at two levels. Purarge aegeria hibernates as a third instar larva or in the pupal stage, cantering one of four major developmental pathways in response to photoperiod: (1) direct development in both the larval and pupal stages, (2) pupal winter diapause with or (3) without a preceding larval summer diapause, or (4) larval winter diapause. In addition to this high-level regulation of individual development, larval growth rate and pupal development rate also appear to be finally regulated by photoperiod within each major pathway. As photoperiods decreased from 22 h to 17 h at 17° C, growth rate among directly developing larvae increased progressively, as was the case for larva? developing according to a univoltine life cycle from 17 h to 14 h. At two photoperiods, 13 h and 16 h (corresponding to shifts between major pathways), both larval and pupal development were extremely variable with the fastest individuals developing directly and the slowest developing with a diapause. This indicates a gradual nature of diapause itself, suggesting that the two level may not he fundamentally different. 相似文献
5.
6.
叶绿体中存在着与细胞分裂素(CTK)专一结合的蛋白质。这一蛋白与6-苄氨基嘌呤(6 BA)的亲和力很强,解离常数达3.7×10~(-8)mol/L。最大结合量为10.7 pmol 6 BA/mg蛋白,Seatchard分析表明只有一类结合位点。不同的叶绿体纯化步骤对CTK结合蛋白的活性有不同的影响,分离步骤少而快速的差速离心法可以得到具有较高结合活性的叶绿体。叶绿体经分离纯化后,低温保存时的结合活性较稳定,-20℃以下可以较长期保存。用EDTA预处理叶绿体,不降低CTK结合蛋白对6 BA的结合活性,而用高浓度的NaCl处理,可以使叶绿体结合6BA的能力明显下降。这说明EDTA不能使CTK结合蛋白从叶绿体膜系统表面解离,而高浓度NaCl则有这种可能性。 相似文献
7.
8.
9.
本文报道跃度蝗属1新种。模式标本保存于东北师范大学生物系动物标本室。1.土们岭跃度蝗Podismopsis tumenlingensis,新种 雄性:体小型。头顶三角形,具中隆线,眼间距宽为触角间颜面隆起宽的2.00-2.26倍。缺头侧窝。颜面倾斜,颜面隆起侧缘近平行,中央具纵沟。触角丝状, 相似文献
10.
Mu-Chin Tzeng Ming Jhy Hseu Jun Hai Yang Richard John Guillory 《The protein journal》1986,5(3):221-228
Snake presynaptic toxins such as crotoxin, β-bungarotoxin and taipoxin block neuromuscular transmission through inhibiting the release of acetylcholine by their phospholipase A2 activities. On the other hand, many other phospholipase A2s show little neurotoxicity. It is likely that the difference lies in whether high affinity binding to nerve cell membranes exists or not. To test this idea, crotoxin, β-bungarotoxin and taipoxin were first radioactively labeled with Na(125I) without loss of their neurotoxicity. Using the radioactive toxins we have found that each of the three showed specific binding to synaptosomal membranes from guinea pig brain. In contrast, we could not detect specific binding of a non-neurotoxic pancreatic phospholipase A2. Crotoxin and taipoxin, but not β-bungarotoxin, also bound specifically to membrane preparation from other tissues. The binding of each toxin was not greatly affected by the other two toxins. The photoaffinity labeling technique has been used to obtain further information about the components which bind crotoxin. For this purpose, (125I) crotoxin was derivatized with N-hydroxysuccinimidyl-4-azidobenzoate. Autoradiographic analysis of the membranes following photoirradiation in the presence of the modified crotoxin revealed that an 85K dalton component was preferentially covalently conjugated with the crotoxin analogue in a specific manner. 相似文献