全文获取类型
收费全文 | 11368篇 |
免费 | 1100篇 |
国内免费 | 91篇 |
出版年
2022年 | 69篇 |
2021年 | 232篇 |
2020年 | 149篇 |
2019年 | 193篇 |
2018年 | 228篇 |
2017年 | 204篇 |
2016年 | 357篇 |
2015年 | 598篇 |
2014年 | 581篇 |
2013年 | 722篇 |
2012年 | 911篇 |
2011年 | 858篇 |
2010年 | 522篇 |
2009年 | 491篇 |
2008年 | 653篇 |
2007年 | 580篇 |
2006年 | 551篇 |
2005年 | 530篇 |
2004年 | 434篇 |
2003年 | 392篇 |
2002年 | 333篇 |
2001年 | 291篇 |
2000年 | 264篇 |
1999年 | 218篇 |
1998年 | 104篇 |
1997年 | 74篇 |
1996年 | 84篇 |
1995年 | 71篇 |
1994年 | 60篇 |
1993年 | 74篇 |
1992年 | 142篇 |
1991年 | 108篇 |
1990年 | 107篇 |
1989年 | 118篇 |
1988年 | 86篇 |
1987年 | 91篇 |
1986年 | 93篇 |
1985年 | 93篇 |
1984年 | 73篇 |
1983年 | 70篇 |
1982年 | 60篇 |
1981年 | 53篇 |
1980年 | 49篇 |
1979年 | 82篇 |
1978年 | 63篇 |
1977年 | 53篇 |
1976年 | 49篇 |
1975年 | 41篇 |
1974年 | 48篇 |
1973年 | 44篇 |
排序方式: 共有10000条查询结果,搜索用时 265 毫秒
31.
In classical t(9;22) translocation, as observed in chronic granulocytic leukemia (CGL), a hybrid DNA unit is produced, including a rearranged PHL gene, previously known as bcr (breakpoint cluster region) plus the translocated c-abl gene from chromosome 9: a hybrid bcr-abl protein, p210 is formed, with increased tyrosine kinase activity. Such DNA rearrangement, with a p210 protein synthesis, is also found in cases of Philadelphia-positive acute lymphoblastic leukemia (ALL), but in apparently similar cases the bcr gene is not rearranged, and a novel p190 abl-related protein can be found; c-abl rearrangement has also been observed.It is thus established that correlations between cytogenetic and molecular events can be found in CGL and ALL, as in other haemopoietic malignancies: translocation and possible rearrangement of the c-abl oncogene seem of particular importance in this case. 相似文献
32.
Molecular isolation and sequence determination of the cDNA for the mouse sperm-specific lactate dehydrogenase-X gene 总被引:3,自引:0,他引:3
K C Wu K Chan C Y Lee Y F Lau 《Biochemical and biophysical research communications》1987,146(3):964-970
Several cDNA clones for the mouse lactate dehydrogenase-X (LDH-X), a sperm-specific glycolytic enzyme, were isolated from mouse testicular cDNA libraries constructed in the bacteriophage vectors, lambda gt11 and gt10. The largest cDNA clone contains an insert of 1135 base pairs in length and an open reading frame that encodes a 332 amino acid polypeptide with a molecular weight of 35.89 kD. The deduced amino acid sequence of this protein is in close agreement with the published sequence of mouse LDH-X obtained by direct protein sequencing. Northern analysis of RNA isolated from different tissues detected a single size mRNA of 1.5 kilobases in mouse testis but not in brain or liver. The Ldh-x structural gene was estimated to be about 12 kb in size as demonstrated by Southern hybridization analysis of mouse genomic DNA using the full-length cDNA as a probe. 相似文献
33.
Liver microsomal membrane fluidity and lipid characteristics in vitamin A-deficient rats. 总被引:2,自引:0,他引:2 下载免费PDF全文
Rat liver microsomes (microsomal fraction) were isolated from vitamin A-deficient and -sufficient rats and analysed for membrane lipid characteristics. Membrane fluidity was found to be significantly decreased in microsomes from the vitamin A-deficient rats, but not in liposomes prepared from lipid extracts. Microsomes from vitamin A-deficient animals showed a significant decrease in C18:2, omega 6 and an increase in C22:5, omega 6 fatty acids. 相似文献
34.
Latika P. Chanderkar Gouri Shanker Robert L. Knobler Fred D. Lublin Woon Ki Paik Sangduk Kim 《Neurochemical research》1987,12(5):445-449
Mice with the dysmyelinating mutation shiverer were studied by measuring the activity of two protein methylases and myelin marker enzymes in the brain. It was observed thatS-adenosylmethionine: protein-lysineN-methyltransferase (protein methylase III, EC. 2.1.1.43) activity is significantly reduced in phenotypically affected homozygous shiverer (shi/shi) mutant mouse brain compared to the unaffected heterozygous littermate brain. This reduction in enzyme activity is manifested mainly by reduced formation of trimethyllysine during the in vitro methylation of histone. In contrast, myelin marker enzymes such as 2,3-cyclic nucleotide 3-phosphohydrolase and 5-nucleotidase as well asS-adenosyl-methionine: protein-carboxylO-methyltransferase (protein methylase II, EC. 2.1.1.24) activities were not significantly affected in these strains of mice. 相似文献
35.
36.
Isolation and expression of an anther-specific gene from tomato 总被引:31,自引:0,他引:31
David Twell Rod Wing Judy Yamaguchi Sheila McCormick 《Molecular & general genetics : MGG》1989,217(2-3):240-245
37.
Summary The distribution, frequency and size of neuroepithelial bodies (NEB) were studied in lungs of rabbits during different stages of development (27-day fetus, newborn, 6, 11, 21, 28 and 56 days postnatally). NEB were visualized by immunostaining with monoclonal antibody against serotonin. Detailed quantitiation of NEB was performed by use of camera lucida drawings of immunostained serial sections from the same anatomical region, i.e. the lower lobe of the left lung. The total number of NEB was counted and expressed per epithelial length of airway, surface area and volume. The size of NEB defined as surface area as well as the position of NEB in relation to the airway bifurcations was assessed in airways of different sizes. The overall number and size of NEB were found to increase during the immediate perinatal period followed by a sharp decline at 56 days of age. The number of NEB peaked at 6 days postnatally (mean 175.5 NEB/mm3 of airway epithelium) and declined significantly (3.0 NEB/mm3) at 56 days of postnatal age. The size of NEB reached its maximum at 11 days (mean surface area 659.54 m2, with the largest NEB measuring 1839.98 m2). By 56 days of age, NEB became significantly smaller (mean surface area 177.29 m2) consisting of small clusters of cells situated deep within the airway epithelium. At all ages, about half of all NEB (mean 47.6%) were localized within the small peripheral airways with up to 63.9% located at airway bifurcations. These findings indicate that the functional activity of NEB may be confined predominantly to the perinatal period. The postulated functions of NEB include those of intrapulmonary hypoxia-sensitive chemoreceptors and/or endocrine-paracrine activity in the lung. Such function(s) may be important during adaptation to extrauterine life as well as for growth and development of the lung. 相似文献
38.
Err-Cheng Chan Peter Pear Ueng Li Fu Chen 《Applied microbiology and biotechnology》1989,31(5-6):524-528
Summary The Escherichia coli xylose isomerase gene was transformed into Schizosaccharomyces pombe for direct d-xylose utilization. In order to understand d-xylose metabolism and determine the limiting factors on d-xylose utilization by the transformed yeast, d-xylose transport, xylose isomerization, and xylulose phosphorylation were investigated. The results indicated that low activity of xylose isomerization in the cloned yeast was the limiting step for d-xylose fermentation. An in vitro study showed that yeast proteases decreased xylose isomerase activity. Xylitol, a by-product of d-xylose fermentation, had no effect on the activity of xylose isomerase. 相似文献
39.
The primary structure of rat ribosomal protein L18a 总被引:3,自引:0,他引:3
The amino acid sequence of rat ribosomal protein L18a was deduced from the sequence of nucleotides in a recombinant cDNA. Ribosomal protein L18a contains 175 amino acids and has a molecular mass of 20,047 Da. Hybridization of the cDNA to digests of rat nuclear DNA and to a preparation of poly(A)+ mRNA suggests that there are 8-11 copies of the L18a gene and that the mRNA for the protein is about 700 nucleotides in length. Rat L18a is related to Schizosaccharomyces pombe L17 and perhaps to Halobacterium marismortui L19. 相似文献
40.
Soluble derivatives of the beta amyloid protein precursor of Alzheimer's disease are labeled by antisera to the beta amyloid protein 总被引:6,自引:0,他引:6
M R Palmert S L Siedlak M B Podlisny B Greenberg E R Shelton H W Chan M Usiak D J Selkoe G Perry S G Younkin 《Biochemical and biophysical research communications》1989,165(1):182-188
The amyloid deposited in Alzheimer's disease (AD) is composed primarily of a 39-42 residue polypeptide (beta AP) that is derived from a larger beta amyloid protein precursor (beta APP). In previous studies, we and others identified full-length, membrane-associated forms of the beta APP and showed that these forms are processed into soluble derivatives that lack the carboxyl-terminus of the full-length forms. In this report, we demonstrate that the soluble approximately 125 and approximately 105 kDa forms of the beta APP found in human cerebrospinal fluid are specifically labeled by several different antisera to the beta AP. This finding indicates that both soluble derivatives contain all or part of the beta AP sequence, and it suggests that one or both of these forms may be the immediate precursor of the amyloid deposited in AD. 相似文献