全文获取类型
收费全文 | 3594篇 |
免费 | 412篇 |
国内免费 | 1868篇 |
专业分类
5874篇 |
出版年
2024年 | 57篇 |
2023年 | 163篇 |
2022年 | 242篇 |
2021年 | 248篇 |
2020年 | 206篇 |
2019年 | 215篇 |
2018年 | 178篇 |
2017年 | 162篇 |
2016年 | 180篇 |
2015年 | 222篇 |
2014年 | 309篇 |
2013年 | 278篇 |
2012年 | 329篇 |
2011年 | 365篇 |
2010年 | 264篇 |
2009年 | 269篇 |
2008年 | 318篇 |
2007年 | 288篇 |
2006年 | 232篇 |
2005年 | 237篇 |
2004年 | 182篇 |
2003年 | 150篇 |
2002年 | 154篇 |
2001年 | 126篇 |
2000年 | 117篇 |
1999年 | 65篇 |
1998年 | 36篇 |
1997年 | 17篇 |
1996年 | 23篇 |
1995年 | 15篇 |
1994年 | 21篇 |
1993年 | 25篇 |
1992年 | 13篇 |
1991年 | 14篇 |
1990年 | 15篇 |
1989年 | 13篇 |
1988年 | 9篇 |
1987年 | 6篇 |
1986年 | 9篇 |
1985年 | 9篇 |
1984年 | 6篇 |
1983年 | 5篇 |
1979年 | 4篇 |
1978年 | 5篇 |
1974年 | 5篇 |
1966年 | 4篇 |
1959年 | 5篇 |
1958年 | 7篇 |
1957年 | 9篇 |
1956年 | 5篇 |
排序方式: 共有5874条查询结果,搜索用时 10 毫秒
1.
Samples of marine pleuston were collected from the sea-surface along considerable sections of the track of Eye of the Wind during its 2-year circumnavigational expedition 'Operation Drake' from November 1978 to October 1980. One hundred and eleven of the tow samples contained insects of the genus Halobates . They were assigned to four oceanic species: H. micans, H. sericeus, H. germanus and H. splendens; two coastal species: H. maculatus, H. princeps, and one undescribed species. Various development stages of the oceanic species were found. The locations, time of collection and surface temperatures where sea-skaters were collected are tabulated. Distributional boundaries and population densities of the oceanic species collected are discussed. 相似文献
2.
Hongchi Yu Yang Shen Jingsi Jin Yingying Zhang Tang Feng 《Cell Adhesion & Migration》2018,12(1):56-68
Hepatocellular carcinoma (HCC) is a subtype of malignant liver cancer with poor prognosis and limited treatment options. It is noteworthy that mechanical forces in tumor microenvironment play a pivotal role in mediating the behaviors and functions of tumor cells. As an instrumental type of mechanical forces in vivo, fluid shear stress (FSS) has been reported having potent physiologic and pathologic effects on cancer progression. However, the time-dependent mechanochemical transduction in HCC induced by FSS remains unclear. In this study, hepatocellular carcinoma HepG2 cells were exposed to 1.4 dyn/cm2 FSS for transient duration (15s and 30s), short duration (5 min, 15 min and 30 min) and long duration (1h, 2h and 4h), respectively. The expression and translocation of Integrins induced FAK-Rho GTPases signaling events were examined. Our results showed that FSS endowed HepG2 cells with higher migration ability via reorganizing cellular F-actin and disrupting intercellular tight junctions. We further demonstrated that FSS regulated the expression and translocation of Integrins and their downstream signaling cascade in time-dependent patterns. The FSS downregulated focal adhesion components (Paxillin, Vinculin and Talin) while upregulated the expression of Rho GTPases (Cdc42, Rac1 and RhoA) in long durations. These results indicated that FSS enhanced tumor cell migration through Integrins-FAK-Rho GTPases signaling pathway in time-dependent manners. Our in vitro findings shed new light on the role of FSS acting in physiologic and pathological processes during tumor progression, which has emerged as a promising clinical strategy for liver carcinoma. 相似文献
3.
Restructured beef steaks, formulated with different beef particle sizes, fat content and binder levels, were evaluated with selected marketing factors by 30 consumers. Conjoint analysis was applied to consumers’hedonic scores and statement of purchase intent for raw and cooked steaks. Product preference, packaging and brand had significant (P < 0.05) impacts on hedonic scores for raw products. Price was an additional important factor in purchase intent. Parcooked products, only product preference was important for both hedonic rating and purchase intent. When products were not present, conjoint measurement indicated that nutritional information, price and brand influenced (P < 0.05) hedonic responses. 相似文献
4.
5.
A single wheatgrass chromosome reduces the concentration of barley yellow dwarf virus in wheat 总被引:3,自引:0,他引:3
R. I. S. BRETTELL P. M. BANKS Y. CAUDERON X. CHEN Z. M. CHENG P. J. LARKIN P. M. WATERHOUSE 《The Annals of applied biology》1988,113(3):599-603
Seedlings of a series of addition or substitution lines of wheat containing different Thinopyrum intermedium chromosomes were inoculated with the PAV and RPV serotypes of barley yellow dwarf virus (BYDV). Reduced virus titres in infected plants were ascribed to a single pair of homoeologous group 7 chromosomes from Th. intermedium in the disomic addition lines L1 and TAF 2. The group 7 chromosome is associated with red pigmentation of coleoptiles, which was also observed in two lines ditelosomic for the α arm of the chromosome. However, when infected with the PAV serotype of BYDV, the ditelosomic lines had normal virus titres and it is concluded that potential determinants of BYDV resistance are located on the β arm of the Group 7 chromosome. 相似文献
6.
本文用5-氮氧自由基硬脂酸、12-氮??氧自由基硬脂酸和16-氮氧自由基硬脂酸三种脂肪酸自旋标记物对人红细胞膜(血影)的不同深度膜脂的流动性作了进一步的研究,所得到的电子自旋共振波谱表明它们的序参数都随γ照射剂量的增大而增大。本文还用马来酰亚胺氮氧自由基标记在膜蛋白的SH基团上,所得到的波谱表明其旋转相关时间和强固定化对弱固定化组分的谱线高度的比值也都随γ辐照剂量增大而增大。结果说明γ辐照后,人红细胞膜的流动性降低。这与我们用荧光探针研究所得到的结果相似。 相似文献
7.
超干处理对几种芸苔属植物种子生理生化和细胞超微结构的效应 总被引:1,自引:0,他引:1
几种芸苔属植物种子经过超干处理后,发芽力和活力不受影响,耐藏性大为提高。超干及老化后种子的脱氢酶、超氧物歧化酶、过氧化物酶、过氧化氢酶等酶系统保持完好;丙二醛和挥发性醛类物质等劣变产物相应减少;电导率测定表明,细胞膜系统的完整性良好;透射电镜(TEM)和扫描电镜(SEM)观察表明,细胞超微结构及功能保持完好。不同干燥方法和不同干燥剂的系列实验证实,生石灰的脱水效果并不亚于冰冻真空干燥法,且经济实用。 相似文献
8.
9.
在浅麻醉大鼠上,在延髓腹内侧结构内观察到三种具有不同放电类型的细胞,即乃尾前放电骤停的撤反应细胞,甩尾前放电骤增的给反应细胞和甩尾无关的中性细胞。电刺激外侧缰核可抑制撤反应细胞的自发放电,加强给反应细胞自发放电,从而易化两类细胞的甩尾相关反应,同时易化伤害刺激引起的甩尾反射。实验结果说明,外侧缰核对节段性防御反射有易化作用,这种易化作用可能是通过延髓内撤反应和反应细胞的协同活动而实现的。 相似文献
10.
利用标记基因选配褐壳蛋鸡配套杂交亲本 总被引:5,自引:0,他引:5
程光潮 刘树俊 段章雄 张琦 王力 刘坤凡CHENG Guang-Chao LIU Shu-Jun DUAN Zhang-Xiong ZHANG Qi WANG Li LIU Kun-Fan 《遗传》1996,18(2):28-32
应用本实验室研制的抗鸡红细胞抗原单价血清(4个位点, 14个等位基因)和DNA指纹技术,对我们组配成功的一个褐壳蛋鸡配套系统的5个亲本进行了群体遗传学分析。结果表明,由标记基因测定所提供的亲本品系遗传差异的大小, 与这些品系实际杂交效果的优劣相一致,证实了标记辅助选种方法有的效性。 相似文献