全文获取类型
收费全文 | 8864篇 |
免费 | 566篇 |
国内免费 | 8篇 |
专业分类
9438篇 |
出版年
2022年 | 49篇 |
2021年 | 94篇 |
2020年 | 46篇 |
2019年 | 61篇 |
2018年 | 106篇 |
2017年 | 85篇 |
2016年 | 136篇 |
2015年 | 260篇 |
2014年 | 311篇 |
2013年 | 407篇 |
2012年 | 485篇 |
2011年 | 476篇 |
2010年 | 314篇 |
2009年 | 305篇 |
2008年 | 483篇 |
2007年 | 488篇 |
2006年 | 477篇 |
2005年 | 518篇 |
2004年 | 463篇 |
2003年 | 405篇 |
2002年 | 369篇 |
2001年 | 231篇 |
2000年 | 254篇 |
1999年 | 241篇 |
1998年 | 115篇 |
1997年 | 103篇 |
1996年 | 82篇 |
1995年 | 96篇 |
1994年 | 71篇 |
1993年 | 88篇 |
1992年 | 180篇 |
1991年 | 166篇 |
1990年 | 139篇 |
1989年 | 142篇 |
1988年 | 152篇 |
1987年 | 95篇 |
1986年 | 86篇 |
1985年 | 107篇 |
1984年 | 93篇 |
1983年 | 76篇 |
1982年 | 53篇 |
1981年 | 62篇 |
1980年 | 34篇 |
1979年 | 47篇 |
1978年 | 45篇 |
1977年 | 38篇 |
1976年 | 29篇 |
1975年 | 47篇 |
1974年 | 46篇 |
1973年 | 40篇 |
排序方式: 共有9438条查询结果,搜索用时 11 毫秒
1.
The precipitation of tobacco mosaic virus by sodium chondroitin sulfate in an aqueous solution was investigated kinetically by means of turbidimetry. The virus solution became turbid after the addition of chondroitin sulfate. A threshold concentration of chondroitin, 1.33 mg/ml, was required for virus precipitation, irrespective of the virus concentration. The precipitation resulted from a mutual spatial exclusion phenomenon, leading to the separation of the virus as a crystalline phase. The dimension of chondroitin sulfate calculated at the threshold concentration agreed well with that obtained by other methods. The initial slopes and the aggregation half-times of the virus aggregates depended on both chondroitin and virus concentrations and the former increased with the increase in concentration of each. Above the threshold concentration of chondroitin sulfate, tobacco mosaic virus aggregation was a rapid-aggregation process and ended within 100 sec. 相似文献
2.
Histone deacetylase from calf thymus 总被引:4,自引:0,他引:4
3.
A congenital diverticulum of the ileum (Meckel's diverticulum), approximately 10 mm long, was detected in a rat and examined histologically. The histological findings were basically the same as in the ileum. Although Meckel's diverticulum is uncommon in the rat, the present report demonstrated the possibility of discovering new cases. 相似文献
4.
Masaru Kubota Ying-Wei Lin Keigo Hamahata Machiko Sawada Seiji Koishi Haruyo Hirota Yoshihiro Wakazono 《Mutation Research - Genetic Toxicology and Environmental Mutagenesis》2000,470(2):21
The occurrence of a second neoplasm is one of the major obstacles in cancer chemotherapy. The elucidation of the genotoxic effects induced by anti-cancer drugs is considered to be helpful in identifying the degree of cancer risk. Numerous investigations on cancer patients after chemotherapy have demonstrated: (i) an increase in the in vivo somatic cell mutant frequency (Mf) at three genetic loci, including hypoxanthine–guanine phosphoribosyl-transferase (hprt), glycophorin A (GPA), and the T-cell receptor (TCR), and (ii) alterations in the mutational spectra of hprt mutants. However, the time required for and the degree of such changes are quite variable among patients even if they have received the same chemotherapy, suggesting the existence of underlying genetic factor(s). Accordingly, some cancer patients prior to chemotherapy as well as patients with cancer-prone syndrome have been found to show an elevated Mf. Based on the information obtained from somatic cell mutation assays, an individualized chemotherapy should be considered in order to minimize the risk of a second neoplasm. 相似文献
5.
6.
Koichi Inoue Akiko Yamaguchi Megumi Wada Yoshihiro Yoshimura Tsunehisa Makino Hiroyuki Nakazawa 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》2001,765(2):3469-126
Due to the ubiquity of epoxy resin compounds and their potential role in increasing the risk for reproductive dysfunction and cancer, the need for an assessment of human exposure is urgent. Therefore, we developed a method for measuring bisphenol A (BPA) and bisphenol A diglycidyl ether (BADGE) metabolites in human blood samples using high-performance liquid chromatography–electrospray ionization mass spectrometry (LC–MS). Human blood samples were processed using enzymatic deconjugation of the glucuronides followed by a novel sample preparation procedure using a solid-phase-cartridge column. This selective analytical method permits rapid detection of the metabolites, free BPA and a hydrolysis product of BADGE (BADGE-4OH) with detection limits in the low nanogram per milliliter range (0.1 ng ml−1 of BPA and 0.5 ng ml−1 of BADGE-4OH). The sample extraction was achieved by Oasis HLB column on gradient elution. The recoveries of BPA and BADGE-4OH added to human plasma samples were above 70.0% with a standard deviation of less than 5.0%. This selective, sensitive and accurate method will assist in elucidating potential associations between human exposure to epoxy-based compounds and adverse health effects. 相似文献
7.
Hisao Tsukamoto Yoshihiro Kubo David L. Farrens Mitsumasa Koyanagi Akihisa Terakita Yuji Furutani 《The Journal of biological chemistry》2015,290(45):27176-27187
Melanopsins play a key role in non-visual photoreception in mammals. Their close phylogenetic relationship to the photopigments in invertebrate visual cells suggests they have evolved to acquire molecular characteristics that are more suited for their non-visual functions. Here we set out to identify such characteristics by comparing the molecular properties of mammalian melanopsin to those of invertebrate melanopsin and visual pigment. Our data show that the Schiff base linking the chromophore retinal to the protein is more susceptive to spontaneous cleavage in mammalian melanopsins. We also find this stability is highly diversified between mammalian species, being particularly unstable for human melanopsin. Through mutagenesis analyses, we find that this diversified stability is mainly due to parallel amino acid substitutions in extracellular regions. We propose that the different stability of the retinal attachment in melanopsins may contribute to functional tuning of non-visual photoreception in mammals. 相似文献
8.
H Kobayashi A Inoue T Mikawa H Kuwayama Y Hotta T Masaki S Ebashi 《Journal of biochemistry》1992,112(6):786-791
Two proteins with myosin light chain kinase activity and electrophoretic molecular weights of 155,000 and 130,000 were each isolated from bovine stomach smooth muscle [Kuwayama, H., Suzuki, M., Koga, R., & Ebashi, S. (1988) J. Biochem. 104, 862-866]. The 155 kDa component showed a much higher superprecipitation-inducing activity than the 130 kDa component, when compared on the basis of equivalent myosin light chain kinase activity. In this study, we isolated a cDNA for the entire coding region of the 155 kDa protein. The deduced amino acid sequence revealed a high degree of similarity to those of chicken and rabbit smooth muscle myosin light chain kinases. Multiple motifs, such as three repeats of an immunoglobulin C2-like domain, a fibronectin type III domain, and unusual 20 repeats of 12 amino acids were detected in the sequence. Part of the amino-terminal sequence was similar to that of the actin- and calmodulin-binding domain of smooth muscle caldesmon. These observations suggest that the 155 kDa protein has additional functions other than its enzymatic activity. Two mRNAs of 6.0 and 2.6 kb in length in the bovine stomach smooth muscle RNAs were hybridized with cDNA probes. The 2.6-kb RNA probably encodes telokin, which is the carboxyl terminus of smooth muscle myosin light chain kinase. mRNAs with identical lengths were also detected in bovine aorta. 相似文献
9.
We studied settling-site selection and the resulting survival of two sessile scale insects, Ceroplastes rubens and C. ceriferus, in the citrus tree, Citrus unshiu, in central Japan. C. rubens preferred 0-year-old twigs most as a settling-site; the density of nymphs settling on 0-year-old twigs was significantly higher than those on ≥1-year-old twigs, and few nymphs settled on ≥3-year-old twigs. The mean survival rates from settling until reproduction in the next year were significantly higher on more preferred twigs than on less preferred ones. In C. ceriferus, nymphs significantly preferred 1- and 2-year-old twigs to 0- and ≥3-year-old ones, and the mean survival rates on the more preferred 1- and 2-year-old twigs were significantly higher than those on less preferred ≥3-year-old twigs. However, the survival rate on less preferred 0-year-old twigs was slightly higher than those on 1- and 2-year-old ones. Thus, in both species of scale, it was the preferred twigs which were more profitable sites for survival after settling, except for less preferred 0-year-old twigs for C. ceriferus. In both scale species, most mortality was due to growth cessation, which is believed to be related to the twig quality as a food source. Predators and parasitoids were minor mortality factors. Both species showed constant survival rates until the density of settled nymphs exceeded double the “upper-limit” density, whereupon they decreased drastically. Nymphs of C. rubens settling on twigs of high scale density showed a spacing-out distribution, those of C. ceriferus did not. In C. rubens, an increase in preference for originally less profitable twigs at the later stage of the settling season was observed, but not in C. ceriferus. Accordingly, individuals of C. rubens showed a stronger tendency to avoid conspecifics than did C. ceriferus. Although nymphs of the two scales clearly preferred more profitable sites, their settling-site selection did not agree with the predictions from the ideal free distribution theory (Fretwell and Lucas, 1970). The discrepancies were (1) frequent settling on less profitable sites at the early stage of the settling season, (2) insufficient utilization of the most profitable twigs, and (3) virtually 100% mortality on overcrowded twigs under conditions where unoccupied profitable twigs still remained. These discrepancies are thought due to the limited dispersal time of nymphs. 相似文献
10.
Junko Maeda Charles R. Yurkon Yoshihiro Fujii Hiroshi Fujisawa Sayaka Kato Colleen A. Brents Mitsuru Uesaka Akira Fujimori Hisashi Kitamura Takamitsu A. Kato 《PloS one》2015,10(12)
When energetic particles irradiate matter, it becomes activated by nuclear reactions. Radioactivation induced cellular effects are not clearly understood, but it could be a part of bystander effects. This investigation is aimed at understanding the biological effects from radioactivation in solution induced by hadron radiation. Water or phosphate buffered saline was activated by being exposed to hadron radiation including protons, carbon- and iron-ions. 1 mL of radioactivated solution was transferred to flasks with Chinese hamster ovary (CHO) cells cultured in 5 mL of complete media. The induction of sister chromatid exchanges (SCE) was used to observe any increase in DNA damage responses. The energy spectrum and the half-lives of the radioactivation were analyzed by NaI scintillation detector in order to identify generated radionuclides. In the radioactivated solution, 511 keV gamma-rays were observed, and their half-lives were approximately 2 min, 10 min, and 20 min. They respectively correspond to the beta+ decay of 15O, 13N, and 11C. The SCE frequencies in CHO cells increased depending on the amount of radioactivation in the solution. These were suppressed with a 2-hour delayed solution transfer or pretreatment with dimethyl sulfoxide (DMSO). Our results suggest that the SCE induction by radioactivated solution was mediated by free radicals produced by the annihilated gamma-rays. Since the SCE induction and DMSO modulation are also reported in radiation-induced bystander effects, our results imply that radioactivation of the solution may have some contribution to the bystander effects from hadron radiation. Further investigations are required to assess if radioactivation effects would attribute an additional level of cancer risk of the hadron radiation therapy itself. 相似文献