全文获取类型
收费全文 | 2430篇 |
免费 | 164篇 |
出版年
2021年 | 21篇 |
2020年 | 18篇 |
2019年 | 21篇 |
2018年 | 34篇 |
2017年 | 35篇 |
2016年 | 39篇 |
2015年 | 51篇 |
2014年 | 64篇 |
2013年 | 100篇 |
2012年 | 128篇 |
2011年 | 116篇 |
2010年 | 71篇 |
2009年 | 66篇 |
2008年 | 107篇 |
2007年 | 105篇 |
2006年 | 106篇 |
2005年 | 129篇 |
2004年 | 98篇 |
2003年 | 108篇 |
2002年 | 108篇 |
2001年 | 73篇 |
2000年 | 86篇 |
1999年 | 86篇 |
1998年 | 42篇 |
1997年 | 33篇 |
1996年 | 33篇 |
1995年 | 27篇 |
1994年 | 28篇 |
1993年 | 25篇 |
1992年 | 57篇 |
1991年 | 41篇 |
1990年 | 57篇 |
1989年 | 46篇 |
1988年 | 43篇 |
1987年 | 31篇 |
1986年 | 28篇 |
1985年 | 29篇 |
1984年 | 32篇 |
1983年 | 13篇 |
1981年 | 12篇 |
1980年 | 14篇 |
1979年 | 17篇 |
1978年 | 22篇 |
1977年 | 15篇 |
1976年 | 18篇 |
1975年 | 16篇 |
1974年 | 16篇 |
1973年 | 20篇 |
1972年 | 19篇 |
1970年 | 22篇 |
排序方式: 共有2594条查询结果,搜索用时 15 毫秒
51.
Identification of a basic glycoprotein induced by ethylene in primary leaves of azuki bean as a cationic peroxidase. 总被引:1,自引:1,他引:0
Ethylene causes the accumulation of seven different proteins (each designated AZxx according to its molecular mass, xx in kD) in excised primary leaves of azuki bean (Vigna angularis) (F. Ishige, H. Mori, K. Yamazaki, H. Imaseki [1991] Plant Cell Physiol 32: 681-690). A complementary DNA encoding an ethylene-induced basic glycoprotein, AZ42, from azuki bean was cloned and its complete nucleotide sequence was determined. Characterization of the cDNA was accomplished by monitoring expression of an immunoreactive protein in Escherichia coli that harbored the cDNA and by the identification of a partial amino acid sequence that was the same as that determined from the purified protein. An open reading frame (1071 base pairs) in the cDNA encoded a protein of 357 amino acids with a molecular mass of 39.3 kD. The amino acid sequence contained three regions that are highly conserved among peroxidases from eight different plants. Purified AZ42 exhibited peroxidase activity. The basic glycoprotein induced by ethylene was identified as a cationic isozyme of peroxidase. The corresponding mRNA was not present in leaves that had not been treated with ethylene, but it appeared after 1 h of treatment with ethylene and its level increased for the next 15 h. Accumulation of the mRNA was also induced after wounding or treatment with salicylate. The wound-induced increase in the level of the mRNA was suppressed by 2,5-norbornadiene, but the salicylate-induced increase was not. 相似文献
52.
Fumio Yamazaki Ryoko Sone Nobuharu Fujii Haruo Ikegami 《International journal of biometeorology》1993,37(4):212-217
Based on the hypothesis that the relation between sweating rate and body temperature should be different during exercise and rest after exercise, we compared the sweating response during exercise and recovery at a similar body temperature. Healthy male subjects performed submaximal exercise (Experiment 1) and maximal exercise (Experiment 2) in a room at 27° C and 35% relative humidity. During exercise and recovery of 20 min after exercise, esophageal temperature (Tes), mean skin temperature, mean body temperature (
), chest sweating rate (
), and the frequency of sweat expulsion (F
SW) were measured. In both experiments,
andF
SW were clearly higher during exercise than recovery at a similar body temperature (Tes,
).
was similar during exercise and recovery, or a little less during the former, at a similarF
SW. It is concluded that the sweating rate during exercise is greater than that during recovery at the same body temperature, due to greater central sudomotor activity during exercise. The difference between the two values is thought to be related to non-thermal factors and the rate of change in mean skin temperature. 相似文献
53.
Atsushi Hashimoto † Shin Kumashiro † Toru Nishikawa † Takae Oka † Kiyohisa Takahashi † Takashi Mito ‡ Sachio Takashima ‡ Nagafumi Doi § Yoshihiko Mizutani Tatsuji Yamazaki Tsuguo Kaneko Eiji Ootomo# 《Journal of neurochemistry》1993,61(1):348-351
Abstract: We have analyzed free chiral amino acids (aspartate and serine) in the human frontal cortex at different ontogenic stages (from 14 weeks of gestation to 101 years of age) by HPLC with fluorometric detection after derivatization with N-tert -butyl-oxycarbonyl- l -cysteine and o -phthaldialdehyde. Exceptionally high levels of free d -aspartate and d -serine were demonstrated in the fetal cortex at gestational week 14. The ratios of d -aspartate and of d -serine to the total corresponding amino acids were also high, at 0.63 and 0.27, respectively. The concentration of d -aspartate dramatically decreased to a trace level by gestational week 41 and then remained very low during all postnatal stages. In contrast, the frontal tip contained persistently high levels of d -serine throughout embryonic and postnatal life, whereas the d -amino acid content in adolescents and aged individuals was about half of that in the fetuses. Because d -aspartate and d -serine are known to have selective actions at the NMDA-type excitatory amino acid receptor, the present data suggest that these d -amino acids might play a pivotal role in cerebral development and functions that are related to the NMDA receptor. 相似文献
54.
Kazuo Iwaki Norio Okumura Mitsuru Yamazaki 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》1993,619(2)
A rapid and accurate determination of tetracycline antibiotics in human serum by reversed-phase high-performance liquid chromatography with fluorescence detection has been developed, based on protein precipitation in serum. Various reagents for precipitation were investigated, and 24% trichloroacetic acid in methanolic solution gave the maximum recovery (at least 94.3%) and interference-free chromatograms of different three tetracyclines. At a concentration of 0.5 μg/ml, the precision (relative standard deviation) ranged from 1.12 to 1.94%. In the range 0.04–10.0 μg/ml for oxytetracycline and chlorotetracycline and 0.01–10.0 μg/ml for tetracycline, linear responses were observed. The detection limits of this method were 10–35 ng/ml for all three antibiotics. The proposed method was applied to the determination of serum concentrations in subjects receiving tetracycline antibiotics. 相似文献
55.
Summary A model antigen, rabbit immunoglobulin G, was immobilized onto polyester cloth by adsorption. The antigen cloth was reacted with sheep anti-rabbit IgG antibody. Antibody bound to the antigen cloth was nearly quantitatively eluted by saturated MgCl2, whereas a commercial antibody eluent slowly eluted only about 70 % of the antibody. Exposure of antibody to saturated MgCl2 for 30 min resulted in no loss of immunoactivity. Saturated MgCl2, therefore, is an ideal eluent in immunoaffinity purification of antibodies. 相似文献
56.
Carotenogenic mutants ofPhycomyces, which accumulate excess β-carotene or its intermediates, always failed in zygospore development. No improvement occurred
when such mutants were mated together with a helper wild type of the same mating type against the wild type of the opposite
mating type. Addition of excess synthesized pheromone, trisporin B, also failed to improve the zygospore development, though
the mating response was significantly activated in the early stages and abundant zygophores were formed. Exceptional acceleration
of the zygospore development under these experimental conditions occurred in a regulatory albino mutant (carA), which does not accumulate excess intermediate carotenoids. Chemically- or genetically-induced ovarproduction of β-carotene
or lycopene also inhibited the zygospore development. These results imply that the zygospore development ofPhycomyces is maximal when the intracellular amount of β-carotene is optimal (=wild type), and that pheromones act mainly in the early
stages of mating, while other factors such as the cell-to-cell recognition system may also be involved in the later stages.
Intracellular accumulation of excess β-carotene or its intermediates probably disturb such later-stage factors. 相似文献
57.
Molecular Evolution of the Duplicated Amy Locus in the Drosophila Melanogaster Species Subgroup: Concerted Evolution Only in the Coding Region and an Excess of Nonsynonymous Substitutions in Speciation 下载免费PDF全文
From the analysis of restriction maps of the Amy region in eight sibling species belonging to the Drosophila melanogaster species subgroup, we herein show that the patterns of duplication of the Amy gene are almost the same in all species. This indicates that duplication occurred before speciation within this species subgroup. From the nucleotide sequence data, we show a strong within-species similarity between the duplicated loci in the Amy coding region. This is in contrast to a strong similarity in the 5' and 3' flanking regions within each locus (proximal or distal) throughout the species subgroup. This means that concerted evolution occurred only in the Amy coding region and that differentiated evolution between the duplication occurred in the flanking regions. Moreover, when comparing the species, we also found a significant excess of nonsynonymous substitutions. In particular, all the fixed substitutions specific to D. erecta were found to be nonsynonymous. We thus conclude that adaptive protein evolution occurred in the lineage of D. erecta that is a ``specialist' species for host plants and probably also occurs in the process of speciation in general. 相似文献
58.
Hideki Sezutsu Eiji Nitasaka Tsuneyuki Yamazaki 《Molecular & general genetics : MGG》1995,249(2):168-178
LINE-like retrotransposons, the so-called I elements, control the system of I-R (inducer-reactive) hybrid dysgenesis in Drosophila melanogaster. I elements are present in many Drosophila species. It has been suggested that active, complete I elements, located at different sites on the chromosomes, invaded natural populations of D. melanogaster recently (1920–1970). But old strains lacking active I elements have only defective I elements located in the chromocenter. We have cloned I elements from D. melanogaster and the melanogaster subgroup. In D. melanogaster, the nucleotide sequences of chromocentral I elements differed from those on chromosome arms by as much as 7%. All the I elements of D. mauritiana and D. sechellia are more closely related to the chromosomal I elements of D. melanogaster than to the chromocentral I elements in any species. No sequence difference was observed in the surveyed region between two chromosomal I elements isolated from D. melanogaster and one from D. simulans. These findings strongly support the idea that the defective chromocentral I elements of D. melanogaster originated before the species diverged and the chromosomal I elements were eliminated. The chromosomal I elements reinvaded natural populations of D. melanogaster recently, and were possibly introduced from D. simulans by horizontal transmission. 相似文献
59.
Eiji Nitasaka Tsuneyuki Yamazaki M. M. Green 《Molecular & general genetics : MGG》1995,247(2):164-168
A large proportion of spontaneous mutations inDrosophila melanogaster strains of laboratory origin are associated with insertions of mobile DNA elements. As a first step toward determining whether spontaneous laboratory mutations are predictive for mutational events occurring in the wild, recessivebrown (bw) eye color mutants were isolated. By inbreeding the progeny of wild-caughtDrosophila melanogaster females,bw mutations were isolated from seven separate geographic sites distributed among Japan, California, Siberia and Hungary. Among a total of 14 mutations studied, no case of transposon mutagenesis was found. At least 4 mutations are associated with small deletions in thebw gene. The remainder are inseparable from wild-typebw by Southern analysis and are presumed to be basepair changes or very small indels. Although only two spontaneousbw mutants of laboratory origin have been analyzed molecularly, one is a mobile element insertion. 相似文献
60.
Virulent and avirulent Rhodococcus equi infection in T-cell deficient athymic nude mice: pathologic, bacteriologic and immunologic responses 总被引:1,自引:0,他引:1