全文获取类型
收费全文 | 811758篇 |
免费 | 98763篇 |
国内免费 | 483篇 |
出版年
2018年 | 7150篇 |
2017年 | 6793篇 |
2016年 | 9924篇 |
2015年 | 14588篇 |
2014年 | 16580篇 |
2013年 | 23589篇 |
2012年 | 26782篇 |
2011年 | 27208篇 |
2010年 | 18122篇 |
2009年 | 16710篇 |
2008年 | 23838篇 |
2007年 | 24597篇 |
2006年 | 22599篇 |
2005年 | 22132篇 |
2004年 | 21549篇 |
2003年 | 20931篇 |
2002年 | 20060篇 |
2001年 | 35881篇 |
2000年 | 36142篇 |
1999年 | 28941篇 |
1998年 | 10868篇 |
1997年 | 11398篇 |
1996年 | 10940篇 |
1995年 | 10052篇 |
1994年 | 9990篇 |
1993年 | 9951篇 |
1992年 | 23970篇 |
1991年 | 23124篇 |
1990年 | 22336篇 |
1989年 | 22077篇 |
1988年 | 20041篇 |
1987年 | 19350篇 |
1986年 | 17957篇 |
1985年 | 17916篇 |
1984年 | 15160篇 |
1983年 | 13113篇 |
1982年 | 10375篇 |
1981年 | 9282篇 |
1980年 | 8785篇 |
1979年 | 14307篇 |
1978年 | 11349篇 |
1977年 | 10412篇 |
1976年 | 9773篇 |
1975年 | 10506篇 |
1974年 | 11122篇 |
1973年 | 10997篇 |
1972年 | 9870篇 |
1971年 | 9126篇 |
1970年 | 7607篇 |
1969年 | 7385篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.
82.
Wendy A. Douglass Robert H. Hyland Christopher D. Buckley Aymen Al-Shamkhani Jacqueline M. Shaw Sarah L. Scarth David L. Simmons S.K.Alex Law 《FEBS letters》1998,440(3):125
The cysteine-rich region (CRR) of the β2 integrin subunit was replaced by that of β1 to give the chimera β2NV1. β2NV1 can combine with αL to form a variant leukocyte-function-associated antigen (LFA)-1 on COS cell surface, suggesting that the specificity of the β2 interaction with αL does not lie in the CRR. Unlike those expressing wild-type LFA-1, COS cells expressing αLβ2NV1 are constitutively active in intercellular adhesion molecule (ICAM)-1 adhesion. These results suggest that activation of LFA-1 involves the release of an intramolecular constraint, which is maintained, in part, by the authentic β2 CRR. 相似文献
83.
Grape thaumatin-like proteins (TLPs) play roles in plant-pathogen interactions and can cause protein haze in white wine unless removed prior to bottling. Different isoforms of TLPs have different hazing potential and aggregation behavior. Here we present the elucidation of the molecular structures of three grape TLPs that display different hazing potential. The three TLPs have very similar structures despite belonging to two different classes (F2/4JRU is a thaumatin-like protein while I/4L5H and H2/4MBT are VVTL1), and having different unfolding temperatures (56 vs. 62°C), with protein F2/4JRU being heat unstable and forming haze, while I/4L5H does not. These differences in properties are attributable to the conformation of a single loop and the amino acid composition of its flanking regions. 相似文献
84.
Tomohiro Hamasaki Takahiro Matsumoto Naoya Sakamoto Akiko Shimahara Shiori Kato Ayumi Yoshitake Ayumi Utsunomiya Hisayoshi Yurimoto Esteban C. Gabazza Tadaaki Ohgi 《Nucleic acids research》2013,41(12):e126
Radioisotopes and fluorescent compounds are frequently used for RNA labeling but are unsuitable for clinical studies of RNA drugs because of the risk from radiation exposure or the nonequivalence arising from covalently attached fluorophores. Here, we report a practical phosphoramidite solid-phase synthesis of 18O-labeled RNA that avoids these disadvantages, and we demonstrate its application to quantification and imaging. The synthesis involves the introduction of a nonbridging 18O atom into the phosphate group during the oxidation step of the synthetic cycle by using 18O water as the oxygen donor. The 18O label in the RNA was stable at pH 3–8.5, while the physicochemical and biological properties of labeled and unlabeled short interfering RNA were indistinguishable by circular dichroism, melting temperature and RNA-interference activity. The 18O/16O ratio as measured by isotope ratio mass spectrometry increased linearly with the concentration of 18O-labeled RNA, and this technique was used to determine the blood concentration of 18O-labeled RNA after administration to mice. 18O-labeled RNA transfected into human A549 cells was visualized by isotope microscopy. The RNA was observed in foci in the cytoplasm around the nucleus, presumably corresponding to endosomes. These methodologies may be useful for kinetic and cellular-localization studies of RNA in basic and pharmaceutical studies. 相似文献
85.
D S Faffe G H Silva P M Kurtz E M Negri V L Capelozzi P R Rocco W A Zin 《Journal of applied physiology》2001,90(4):1400-1406
The dynamic mechanical properties of lung tissue and its contents of collagen and elastic fibers were studied in strips prepared from mice instilled intratracheally with saline (C) or silica [15 (S15) and 30 days (S30) after instillation]. Resistance, elastance, and hysteresivity were studied during oscillations at different frequencies on S15 and S30. Elastance increased from C to silica groups but was similar between S15 and S30. Resistance was augmented from C to S15 and S30 and was greater in S30 than in S15 at higher frequencies. Hysteresivity was higher in S30 than in C and S15. Silica groups presented a greater amount of collagen than did C. Elastic fiber content increased progressively along time. This increment was related to the higher amount of oxytalan fibers at 15 and 30 days, whereas elaunin and fully developed elastic fibers were augmented only at 30 days. Silicosis led not only to pulmonary fibrosis but also to fibroelastosis, thus assigning a major role to the elastic system in the silicotic lung. 相似文献
86.
87.
Ca2+ channel antagonist actions in bladder smooth muscle: comparative pharmacologic and [3H]nitrendipine binding studies 总被引:2,自引:0,他引:2
F B Yousif G T Bolger A Ruzycky D J Triggle 《Canadian journal of physiology and pharmacology》1985,63(5):453-462
The actions of a series of 15 Ca2+ channel antagonists including D-600, nifedipine, and diltiazem were examined against K+ depolarization and muscarinic receptor induced responses in guinea pig bladder smooth muscle. Responses of bladder are very dependent upon extracellular Ca2+ and sensitive to the Ca2+ channel antagonists, the tonic component more than the phasic component of response. Regardless of stimulant, K+ or methylfurmethide (MF), or component of response, the same rank order of antagonist activities is expressed, suggestive of a single structure-activity relationship and the existence of a single category of binding site which may, however, exist in several affinity states. High affinity binding of [3H]nitrendipine (KD = 1.1 X 10(-10) M) occurs in bladder membranes, and similar high affinity binding was found in microsomal preparations from other smooth muscles including guinea pig and rat lung, rat vas deferens, uterus, and stomach. [3H]nitrendipine binding in the bladder was sensitive to displacement by other 1,4-dihydropyridines, paralleling their pharmacologic activities and showing excellent agreement with binding data previously obtained for guinea pig ileal smooth muscle. Comparison of pharmacologic data for inhibition of K+- and MF-induced responses by a common series of Ca2+ channel antagonists in bladder and ileum revealed excellent correlations. Neither pharmacologic nor binding studies suggest significant differences in Ca2+ channel antagonist properties in smooth muscle from bladder and intestine. 相似文献
88.
89.
90.