全文获取类型
收费全文 | 748286篇 |
免费 | 80957篇 |
国内免费 | 354篇 |
专业分类
829597篇 |
出版年
2018年 | 6360篇 |
2016年 | 8387篇 |
2015年 | 11175篇 |
2014年 | 13115篇 |
2013年 | 19762篇 |
2012年 | 21596篇 |
2011年 | 22184篇 |
2010年 | 15001篇 |
2009年 | 13912篇 |
2008年 | 19943篇 |
2007年 | 20619篇 |
2006年 | 19616篇 |
2005年 | 18640篇 |
2004年 | 18690篇 |
2003年 | 18052篇 |
2002年 | 17676篇 |
2001年 | 31851篇 |
2000年 | 31948篇 |
1999年 | 25874篇 |
1998年 | 9318篇 |
1997年 | 9867篇 |
1996年 | 9452篇 |
1995年 | 8711篇 |
1994年 | 8738篇 |
1993年 | 8640篇 |
1992年 | 22346篇 |
1991年 | 21725篇 |
1990年 | 21521篇 |
1989年 | 21446篇 |
1988年 | 19839篇 |
1987年 | 18827篇 |
1986年 | 17544篇 |
1985年 | 17997篇 |
1984年 | 14842篇 |
1983年 | 12838篇 |
1982年 | 9807篇 |
1981年 | 8771篇 |
1980年 | 8361篇 |
1979年 | 14232篇 |
1978年 | 11092篇 |
1977年 | 10264篇 |
1976年 | 9843篇 |
1975年 | 10702篇 |
1974年 | 11478篇 |
1973年 | 11182篇 |
1972年 | 10380篇 |
1971年 | 9312篇 |
1970年 | 8108篇 |
1969年 | 7800篇 |
1968年 | 7190篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
21.
22.
Elevated levels of intracellular calcium are a major cause of myocardial dysfunction. To find possible mediators of the deregulated calcium we searched for EF-hand calcium-binding proteins of the S100 family. By PCR technology we identified three members of the S100 protein family (S100 alpha, CACY, and CAPL) in the human heart. We cloned the corresponding cDNAs and examined their expression levels in various human tissues by Northern blot analysis. All three proteins are expressed at high levels in the human heart. Whereas CACY and CAPL mRNAs are expressed ubiquitously, S100 alpha mRNA is restricted to heart, skeletal muscle, and brain. Interestingly, the expression pattern of S100 alpha, CACY, and CAPL in human tissues differs significantly from that in rodent tissues. 相似文献
23.
K I Savitskaia A A Vorob'ev G G Sinitsina 《Zhurnal mikrobiologii, epidemiologii, i immunobiologii》1986,(12):24-31
The results of the inoculation of material taken from the anterior section of the nasal cavity and from the pharyngeal mucosa of 50 healthy young children and 298 acute pneumonia patients were analyzed. 23 microbial species were isolated. In the samples taken from the anterior section of the nasal cavity, monocultures were detected in 86 samples and 54 variants of associations including 2-4 species, in 139 samples. In the samples taken from the pharynx, monocultures were detected in 59 samples and 180 variants of associations including 2-6 species, in 282 samples. Differences in the contamination of the nasal cavity and the pharynx in healthy children and in pneumonia patients were revealed. These differences were manifested in the structure of the microflora (monocultures, associations, their composition), the assortment of microbial species and their concentration. In young children with pneumonia the microflora of the upper respiratory tract was found to reflect the severity of acute pneumonia and the intensity of the pathological process in the lungs (uncomplicated, pyodestructive pneumonia, pyodestructive pneumonia with fatal termination, acute purulent pleurisy). 相似文献
24.
25.
26.
Results are presented on the analysis of three-dimensional motion of compound cilia or cirri in voltage-clamped specimens of the protozoan Stylonychia mytilus. Time series of three-dimensional data were obtained by using the anaxial illumination method for simultaneous recording of stereoscopic video images. Data processing involved the following steps: determination of a reference coordinate system based solely on features present in each stereo-pair; tracing of cirral axes in digitized images, conversion to parameter curves by means of least-squares polynomial approximation, conversion of pairs of two-dimensional data to a series of three-dimensional data; correction for distortion due to projective shortening and conversion to a series of polynomial triplets, and analysis of the periodical components of the motion pattern in the frequency domain. Reconstructed beating cycles show typical differences between hyperpolarization-induced ciliary activity and depolarization-induced ciliary activity. Reconstructions of the motion of the basal segment of a cirrus are in agreement with existing data. Analysis of the curvature and torsion of a cirral axis during beating does not reveal any simple pattern of propagated activity within the axoneme. The return stroke may be subdivided into two phases. First, a curvature peak develops proximally. Secondly, a region with increased torsion arises more distally and spreads out in proximal direction. Both curvature and torsion return to minimal values by the beginning of the power stroke. 相似文献
27.
28.
Immunological characterization of the cytochrome o terminal oxidase from Escherichia coli 总被引:13,自引:0,他引:13
The cytochrome o terminal oxidase from Escherichia coli was immunochemically purified and monospecific antiserum toward cytochrome o was obtained. This antiserum is able to precipitate 100% of the ubiquinol-1 oxidase activity in Triton X-100 extracts of membranes from an E. coli strain in which cytochrome o is the only terminal oxidase. Cytochrome o was analyzed and quantitated using crossed immunoelectrophoresis, rocket immunoelectrophoresis, and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis shows that cytochrome o is composed of four subunits of approximate equimolar stoichiometry with molecular weights of 51,000, 28,500, 18,000, and 12,700. The low temperature (77 K) reduced - oxidized spectrum of the immunoprecipitate shows two peaks at 555 and 562 nm, indicating b-type cytochromes. With the anti-cytochrome o and antiserum toward the cytochrome d terminal oxidase complex which was previously obtained, it is possible to immunochemically assay for all the cytochromes in the cytoplasmic membrane of aerobically grown E. coli. Preliminary results indicate that the biosynthesis of cytochrome o is repressed when cytochrome d is induced by lowering the dissolved oxygen concentration during cell growth. 相似文献
29.
U Mura A M Osman A S Mohamed D Di Martino P L Ipata 《Comparative biochemistry and physiology. B, Comparative biochemistry》1987,87(1):157-160
The preservation of purine ring as purine bases appears to be a common feature of camel liver. Hepatic guanine appears to be actively converted into GMP in the camel rather than further degraded. The limiting step of guanine degradation appears to be the lack of hepatic guanase activity. Higher purine bases over uric acid ratios were found in camel urine with respect to those of zebu. 相似文献
30.
Purification of smooth-muscle myosin free of calmodulin and myosin light-chain kinase. Susceptibility to oxidation. 下载免费PDF全文
Smooth-muscle myosin purified as described by Persechini & Hartshorne [(1983) Biochemistry 22, 470-476] contains trace amounts of calmodulin and myosin light-chain kinase, which can be removed by Ca2+-dependent hydrophobic-interaction chromatography followed by calmodulin-Sepharose affinity chromatography. The resultant column-purified myosin exhibits properties similar to those of the non-purified myosin, e.g. actin activation of the Mg2+-ATPase requires Ca2+/calmodulin-dependent phosphorylation of the two 20 kDa light chains. However, unlike the non-purified myosin, the column-purified myosin undergoes a time-dependent transition to a form which no longer requires phosphorylation for actin activation of the myosin Mg2+-ATPase. This transition is identified as a time-dependent change in conformation of the column-purified myosin from a 10 S to 6 S form and is caused by slow oxidation of the column-purified myosin, since it could be prevented by storage under N2 and reversed by 5 mM-dithiothreitol. 相似文献