全文获取类型
收费全文 | 12679篇 |
免费 | 1256篇 |
国内免费 | 8篇 |
专业分类
13943篇 |
出版年
2022年 | 97篇 |
2021年 | 168篇 |
2020年 | 99篇 |
2019年 | 128篇 |
2018年 | 165篇 |
2017年 | 150篇 |
2016年 | 260篇 |
2015年 | 485篇 |
2014年 | 512篇 |
2013年 | 656篇 |
2012年 | 797篇 |
2011年 | 822篇 |
2010年 | 568篇 |
2009年 | 475篇 |
2008年 | 668篇 |
2007年 | 711篇 |
2006年 | 691篇 |
2005年 | 671篇 |
2004年 | 653篇 |
2003年 | 630篇 |
2002年 | 686篇 |
2001年 | 132篇 |
2000年 | 113篇 |
1999年 | 151篇 |
1998年 | 188篇 |
1997年 | 145篇 |
1996年 | 134篇 |
1995年 | 126篇 |
1994年 | 119篇 |
1993年 | 121篇 |
1992年 | 101篇 |
1991年 | 103篇 |
1990年 | 122篇 |
1989年 | 105篇 |
1988年 | 100篇 |
1987年 | 105篇 |
1986年 | 90篇 |
1985年 | 96篇 |
1984年 | 113篇 |
1983年 | 119篇 |
1982年 | 135篇 |
1981年 | 117篇 |
1980年 | 95篇 |
1979年 | 65篇 |
1978年 | 86篇 |
1977年 | 75篇 |
1976年 | 65篇 |
1975年 | 59篇 |
1974年 | 66篇 |
1973年 | 54篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
Corticosteroid-induced abnormality in fetal mice and H-2 haplotype: Evidence of a cytoplasmic effect
Different strains of H-2 congenic mice have different susceptibilities to corticosteroid-induced fetal loss and cleft palate. Applying this knowledge, we tested the null hypothesis, which assumes that there are no statistically significant differences in the frequency of abnormality among various types of treated backcross offspring and, thus, no evidence of a cytoplasmic effect. In the present study this null hypothesis was frequently, but not consistently, rejected. Therefore, there was some evidence of a cytoplasmic effect. One possible explanation of these results is seen when one considers the phenotypic effects of “gene-gene interaction” between variant H-2 genotypes and an invariant mitochondrial genotype. 相似文献
102.
We have compared the partial nucleotide and derived amino acid sequences of a phaseolin seed storage protein gene ofPhaseolus vulgaris (1) and a conglycinin storage protein gene ofGlycine max (2). Although these proteins are not antigenically related to one another, the architecture of the genes is similar throughout the sequences compared here. Intervening sequences interrupt the same amino acid positions in both genes. Within the 28% of theG. max gene and the 38% of theP. vulgaris gene represented in this comparison, 73% of the nucleotides in the coding and intervening sequences are identical, excluding the insertions and deletions. The nucleotide mismatches found in the coding sequences are distributed throughout the three codon positions with little bias towards the third codon position. In addition to the single nucleotide differences, six insertions or deletions, ranging from three to twenty-seven nucleotides in length, occur in this portion of the coding region and these are partially responsible for the molecular weight differences of the conglycinin α′-subunit and the phaseolin subunit. 相似文献
103.
Otto D. Hensens Ray S. Dewey Jerrold M. Liesch Mary A. Napier Robert A. Reamer Jack L. Smith Georg Albers-Schönberg Irving H. Goldberg 《Biochemical and biophysical research communications》1983,113(2):538-547
Spectroscopic evidence suggests the presence of a highly strained ether ring (Fig. 1) (possibly an epoxide) in the C12-subunit of the previously determined partial structure (Fig. 2) of the major neocarzinostatin chromophore (NCS-Chrom ) which completes assignment of all the oxygens in the molecule. The main product from mercaptan treatment suggests opening of the ether ring involving the addition of one molecule of mercaptan as well as reduction of the C12-substructure, whereas a parallel two-step reduction occurs on NaBH4 treatment. Both reactions occur with rearrangement of the C12-substructure and the implication for the mechanism of action of NCS-Chrom in DNA strand scission activity is discussed. The evidence suggests a downward revision of the molecular formula for NCS-Chrom as well as minor components and by two protons. 相似文献
104.
The effect of continuous-wave ultrasound on the chromosomes of newborn infants has been investigated. Twenty-four women were studied during labour. The fetal heart was monitored by a Sonicaid FM2 monitor applied to the abdomen, and continuous monitoring undertaken for intervals varying from 1 hour 5 minutes to 9 hours 25 minutes. There was no increase in the number of chromosome aberrations in cultures of blood taken from the insonated babies when compared with controls. 相似文献
105.
H. J. Dargie Marjorie E. M. Allison A. C. Kennedy Mary J. B. Gray 《BMJ (Clinical research ed.)》1972,4(5834):196-198
Metolazone is a modified quinazolinesulphonamide and in a dose of between 4 and 7·5 mg is an effective diuretic in man with normal renal function. Fourteen patients with non-oedematous stable chronic renal failure (creatinine clearance ranging from 1·2 to 12 ml/min) were given metolazone in doses ranging from 20-150 mg. A noticeable increase in urine flow and sodium excretion occurred, free water clearance increased, and there was a small but significant increase in potassium excretion. No side effects were noted. 相似文献
106.
Six of the 13 Aeromonas hydrophila, 1 of 10 A. shigelloides, and none of 10 A. salmonicida were found to be psychrophiles. All of the rest of the strains were mesophiles. The mu values (temperature characteristics) could not be used to distinguish psychrophiles from mesophiles. 相似文献
107.
Treatment of rabies virus with the nonionic detergent Nonidet P-40 resulted in solubilization of viral lipids and in a preferential release of the envelope glycoprotein. The other viral proteins and the viral ribonucleic acid remained associated in "core" particles sedimenting at a rate similar to that of intact virions. After fractionation of treated virus by velocity centrifugation in a sucrose density gradient, the amount of residual glycoprotein recovered in the "core" particle fraction and the extent of contamination of the glycoprotein fraction by other viral components were dependent on the ratio of detergent to viral protein used. 相似文献
108.
Isolation and Characterization of Temperature-Sensitive Mutants of Vesicular Stomatitis Virus, New Jersey Serotype 总被引:21,自引:21,他引:0 下载免费PDF全文
Forty-eight temperature-sensitive (ts) mutants have been isolated from a wild-type strain of the New Jersey serotype of vesicular stomatitis virus (VSV) after exposure to the base analogue mutagen 5-fluorouracil. Of these mutants, 47 have been classified into 6 nonoverlapping complementation groups containing 21, 17, 4, 3, 2, and 1 mutant, respectively (1 mutant remaining unallocated). The ribonucleic acid (RNA) phenotype of 23 of these mutants has been established. Four of the six groups contain one or more mutants unable to synthesize detectable amounts of viral RNA under restrictive conditions (39 C). No complementation was observed in mixed infection with ts mutants from the five established complementation groups of the Indiana serotype of VSV. 相似文献
109.
The Distribution of Crossovers along Unreplicated Lambda Bacteriophage Chromosomes 总被引:21,自引:4,他引:17 下载免费PDF全文
Franklin W. Stahl Kenneth D. McMilin Mary M. Stahl Jean M. Crasemann Stephen Lam 《Genetics》1974,77(3):395-408
The distribution of crossovers along unreplicated chromosomes of bacteriophage lambda has been examined by determining the density distributions and genotypes of particles in the progenies of crosses of density-labeled by ordinary parents in the presence of genetic blocks to replication. The Red and Rec systems combined produce crossovers primarily near the ends (especially the right end) of the chromosome. Removal of the generalized lambda recombination functions by red and gam mutations results in loss of these terminal crossovers; coupled with this loss is a disappearance of the differential dependence of recombination frequencies in terminal and central intervals on DNA synthesis. Removal of the bacterial system by a recA mutation results in severe depression of crossing over among unreplicated phage, with the few recombinants produced by the lambda system occurring near the right end. 相似文献
110.
Mary F. Lyon 《Genetics》1974,78(1):305-309