全文获取类型
收费全文 | 4282篇 |
免费 | 268篇 |
国内免费 | 1篇 |
专业分类
4551篇 |
出版年
2022年 | 25篇 |
2021年 | 53篇 |
2020年 | 25篇 |
2019年 | 52篇 |
2018年 | 44篇 |
2017年 | 60篇 |
2016年 | 72篇 |
2015年 | 124篇 |
2014年 | 159篇 |
2013年 | 254篇 |
2012年 | 239篇 |
2011年 | 250篇 |
2010年 | 130篇 |
2009年 | 140篇 |
2008年 | 227篇 |
2007年 | 211篇 |
2006年 | 192篇 |
2005年 | 194篇 |
2004年 | 182篇 |
2003年 | 170篇 |
2002年 | 163篇 |
2001年 | 144篇 |
2000年 | 138篇 |
1999年 | 109篇 |
1998年 | 64篇 |
1997年 | 45篇 |
1996年 | 55篇 |
1995年 | 47篇 |
1994年 | 38篇 |
1993年 | 40篇 |
1992年 | 85篇 |
1991年 | 86篇 |
1990年 | 80篇 |
1989年 | 57篇 |
1988年 | 60篇 |
1987年 | 52篇 |
1986年 | 43篇 |
1985年 | 34篇 |
1984年 | 47篇 |
1983年 | 29篇 |
1982年 | 27篇 |
1981年 | 26篇 |
1980年 | 21篇 |
1979年 | 29篇 |
1978年 | 22篇 |
1977年 | 23篇 |
1976年 | 25篇 |
1974年 | 26篇 |
1973年 | 23篇 |
1972年 | 22篇 |
排序方式: 共有4551条查询结果,搜索用时 0 毫秒
101.
102.
In an attempt to evaluate effects of liver injury and roles of iron metabolism on systemic fungal infection, experimental systemicCandida infection was produced in mice with galactosamine-induced liver injury. Survival rate and extent of fungal lesion are compared between mice with liver injury (Group 1) and ones without liver injury (Group 2). Median survival was 7 and 18 days in Group 1 and 2 respectively after 21 days observation. Mortality rate of Group 1 was significantly higher (P=0.05) than that of Group 2. This difference was reflected to the extent of fungal lesions in that they were extensive and disseminated, involving the multiple organs in Group 1 but predominantly localized to the kidneys in Group 2. UIBC (unbound iron binding capacity) and TIBC (total iron binding capacity), i.e., serum transferrin as well as serum iron levels were significantly lower in Group 1 as compared with those in Group 2. These results indicate that hepatic injury promotesCandida infectionin vivo and suggest that increased susceptibility toCandida in the presence of liver injury is, at least partially, attributable to low UIBC and/or TIBC. 相似文献
103.
Asano R Ikoma K Shimomura I Taki S Nakanishi T Umetsu M Kumagai I 《The Journal of biological chemistry》2011,286(3):1812-1818
Diabodies (Dbs) and tandem single-chain variable fragments (taFv) are the most widely used recombinant formats for constructing small bispecific antibodies. However, only a few studies have compared these formats, and none have discussed their binding kinetics and cross-linking ability. We previously reported the usefulness for cancer immunotherapy of a humanized bispecific Db (hEx3-Db) and its single-chain format (hEx3-scDb) that target epidermal growth factor receptor and CD3. Here, we converted hEx3-Db into a taFv format to investigate how format affects the function of a small bispecific antibody; our investigation included a cytotoxicity assay, surface plasmon resonance spectroscopy, thermodynamic analysis, and flow cytometry. The prepared taFv (hEx3-taFv) showed an enhanced cytotoxicity, which may be attributable to a structural superiority to the diabody format in cross-linking target cells but not to differences in the binding affinities of the formats. Comparable cross-linking ability for soluble antigens was observed among hEx3-Db, hEx3-scDb, and hEx3-taFv with surface plasmon resonance spectroscopy. Furthermore, drastic increases in cytotoxicity were found in the dimeric form of hEx3-taFv, especially when the two hEx3-taFv were covalently linked. Our results show that converting the format of small bispecific antibodies can improve their function. In particular, for small bispecific antibodies that target tumor and immune cells, a functional orientation that avoids steric hindrance in cross-linking two target cells may be important in enhancing the growth inhibition effect. 相似文献
104.
Confirmation of soil-feeding termites (Isoptera; Termitidae; Termitinae) in Australia using stable isotope ratios 总被引:1,自引:1,他引:1
I. Tayasu T. Inoue L. R. Miller A. Sugimoto S. Takeichi & T. Abe 《Functional ecology》1998,12(4):536-542
1. Carbon (δ13 C) and nitrogen (δ15 N) stable isotope ratios of termites (Isoptera) were examined in Darwin, northern Australia. It is suggested that the stable isotope technique, together with phylogenetics, is a useful tool to understand the evolution of functional groups in detritivores.
2. A high δ15 N value was observed in the Termes-Capritermes branch of the subfamily Termitinae and the genus Amitermes , two distinct taxonomic groups that evolved from wood-feeding to soil-feeding in Australia. Among eight Termes-Capritermes branch species, only two species ( Xylochomitermes melvillensis and Ephelotermes melachoma ) were discernible as wood/soil interface feeders, the remaining six species analysed were soil-feeders, where the diet preference was identified by using δ15 N of workers.
3. The Termes-Capritermes group in Australia contains both wood/soil interface feeders and soil-feeders, whereas wood/soil interface feeders in Cameroon are from the Termes-Capritermes branch while soil-feeders are from Cubitermes group. The result confirmed that soil-feeding forms evolved both in Australia and Africa, but from different phylogenetic groups. 相似文献
2. A high δ
3. The Termes-Capritermes group in Australia contains both wood/soil interface feeders and soil-feeders, whereas wood/soil interface feeders in Cameroon are from the Termes-Capritermes branch while soil-feeders are from Cubitermes group. The result confirmed that soil-feeding forms evolved both in Australia and Africa, but from different phylogenetic groups. 相似文献
105.
Takashi Saitoh Jun Osawa Toshikazu Takanishi Shintaro Hayakashi Masaaki Ohmori Toshio Morita Shigeru Uemura Jon Olav Vik Nils Chr. Stenseth Koji Maekawa 《Population Ecology》2007,49(3):249-256
The effects of the abundance of acorns of the oak, Quercus crispula, on the population dynamics of three rodent species (Apodemus speciosus, A. argenteus, and Clethrionomys rufocanus) were analyzed using time series data (1992–2006). The data were obtained in a forest in northern Hokkaido, Japan, by live
trapping rodents and directly counting acorns on the ground. Apodemus speciosus generally increased in abundance following acorn masting. However, the clear effect of acorn abundance was not detected for
the other two rodent species. Acorns of Q. crispula contain tannins, which potentially have detrimental effects on herbivores. Apodemus speciosus may reduce the damage caused by acorn tannins with tannin-binding salivary proteins and tannase-producing bacteria, whereas
such physiological tolerance to tannins is not known in the other two rodent species. The differences in the effects of acorns
between the three species may be due to differences in their physiological tolerance to tannins. 相似文献
106.
107.
Wheat ferredoxin was purified from the leaves of common wheat (Triticum aestivum). The absorption spectrum showed maxima at 465, 425, 332, and 278 nm. The absorbance ratio, A425 nm/A278 nm was 0.49, and the millimolar extinction coefficient at 425 nm was 10.8 mM-1. cm-1. The amino acid composition was determined to be Lys5, His2, Arg1, Asp11, Thr5, Ser7, Glu18, Pro5, Gly6, Ala7, Cys5, Val7, Met1, Ile4, Leu7, Tyr4, Phe1, and Trp1. The total number of amino acid residues was 97. The molecular weight was calculated from the amino acid composition to be 10,829, including iron and sulfur atoms. This value was confirmed by other methods, which were based on the contents of non-heme iron and of terminal amino acid. The N-terminal amino acid was alanine, and the C-terminal amino acid sequence was -Glu-Leu-Thr-AlaCOOH. Comparative studies were performed between T. aestivum ferredoxin and ferredoxins isolated from closely related species; these were T. aegilopoides, T. durum, Ae. squarrosa, and Ae. ovata. No significant differences in the properties of these ferredoxins were detected. It was also shown that these ferredoxins are immunologically homologous. It is, therefore, likely that one molecular species of ferredoxin is distributed through two genera of Triticum and Aegilops. 相似文献
108.
109.
110.
H Tanaka T Shinki T Hayashi C H Jin C Miyaura E Abe T Suda 《Experimental cell research》1989,180(1):72-83
We have reported that 1 alpha,25-dihydroxyvitamin D3 [1 alpha,25(OH)2D3] directly induces fusion of mouse alveolar macrophages by a mechanism involving protein synthesis (H. Tanaka et al., 1984, FEBS Lett. 174, 61). While examining further the mechanism of the fusion, we found that polyamines, most likely spermidine, are involved as an important intracellular mediator of the 1 alpha,25(OH)2D3 action in inducing protein synthesis, which in turn induces fusion of macrophages (T. Hayashi et al., 1986, J. Bone Miner. Res. 1, 235). In this study, spermidine-dependent proteins responsible for inducing fusion were examined by electrophoresis of [35S]methionine-labeled proteins. 1 alpha,25(OH)2D3 increased synthesis of 14 proteins at 24 h after the addition, before it initiated fusion at 36 h. When spermidine synthesis was inhibited by adding methylglyoxal bis(guanylhydrazone) (MGBG), the enhanced synthesis in 9 of the 14 proteins induced by 1 alpha,25(OH)2D3 was greatly diminished with a concomitant inhibition of fusion. Further addition of spermidine restored the synthesis of these 9 proteins and the fusion as well. The synthesis of 3 of the 9 proteins was similarly induced by interferon-gamma, retinoic acid, or lipopolysaccharides, which induced activation but not fusion of macrophages. The apparent molecular weights of the remaining 6 proteins were 142K, 98K, 78K, 60K, 50K, and 42K. Recombinant mouse interleukin 4 (IL-4) also induced fusion of alveolar macrophages by a spermidine-dependent mechanism, and it increased the synthesis of 5 proteins (172K, 98K, 78K, 53K, and 50K). These results suggest that 3 spermidine-dependent proteins (98K, 78K, and 50K) are involved in the fusion of mouse alveolar macrophages induced by 1 alpha,25(OH)2D3 and IL-4. 相似文献