全文获取类型
收费全文 | 1182篇 |
免费 | 96篇 |
国内免费 | 53篇 |
专业分类
1331篇 |
出版年
2024年 | 5篇 |
2023年 | 33篇 |
2022年 | 28篇 |
2021年 | 47篇 |
2020年 | 39篇 |
2019年 | 51篇 |
2018年 | 38篇 |
2017年 | 39篇 |
2016年 | 36篇 |
2015年 | 44篇 |
2014年 | 89篇 |
2013年 | 93篇 |
2012年 | 58篇 |
2011年 | 74篇 |
2010年 | 45篇 |
2009年 | 51篇 |
2008年 | 60篇 |
2007年 | 56篇 |
2006年 | 39篇 |
2005年 | 39篇 |
2004年 | 34篇 |
2003年 | 34篇 |
2002年 | 33篇 |
2001年 | 16篇 |
2000年 | 12篇 |
1999年 | 22篇 |
1998年 | 12篇 |
1997年 | 9篇 |
1996年 | 9篇 |
1995年 | 12篇 |
1994年 | 6篇 |
1993年 | 9篇 |
1992年 | 4篇 |
1991年 | 6篇 |
1990年 | 5篇 |
1988年 | 6篇 |
1986年 | 3篇 |
1985年 | 10篇 |
1984年 | 18篇 |
1983年 | 14篇 |
1982年 | 14篇 |
1981年 | 13篇 |
1980年 | 5篇 |
1979年 | 8篇 |
1978年 | 7篇 |
1977年 | 10篇 |
1976年 | 14篇 |
1975年 | 10篇 |
1974年 | 3篇 |
1973年 | 4篇 |
排序方式: 共有1331条查询结果,搜索用时 15 毫秒
1.
2.
3.
Introduction of T-dependent antigens into the subarachnoid space (isas) resulted in higher systemic antibody responses in mice than injections into the peritoneal cavity (ip) or other sites commonly used for immunization. Antibody production in isas immunized mice was not increased by treatment with cyclophosphamide (Cy) at doses known to abolish T-suppressor-cell activity, but such treatment increased antibody production in ip immunized mice toward the higher level which was observed in the isas immunized animals. Suppressor cell-dependent low zone tolerance (LZT) to TNP-BSA could not be induced by isas injections of deaggregated BSA (d-BSA). Conversely, mice which were unresponsive to ip injected d-BSA showed consistent systemic antibody responses when the antigen was injected isas. These observations indicate that immune responses initiated within the CNS are associated with relatively ineffective induction of systemic suppressor cell activity. 相似文献
4.
The irreversible binding of [2,3-14C]acrylonitrile (VCN) to proteins, RNA and DNA of various tissues of male Sprague-Dawley rats after a single oral dose of 46.5 mg/kg (0.5 LD50) has been studied. Proteins were isolated by chloroform-isoamyl alcohol-phenol extraction. RNA and DNA were separated by hydroxyapatite chromatography. Binding of VCN to proteins was extensive and was time dependent. Radioactivity in nucleic acids was registered in the liver and the target organs, stomach and brain. DNA alkylation, which increased by time, was significantly higher in the target organs, brain and stomach (119 and 81 pmol/mg, respectively, at 24 h) than that in the liver. The covalent binding indices for the liver, stomach and brain at 24 h after dosing were, 5.9, 51.9 and 65.3, respectively. These results suggest that VCN is able to act as a multipotent carcinogen by alkylation of DNA in the extrahepatic target tissues, stomach and brain. 相似文献
5.
Immunologic and clinical improvement of progressive coccidioidomycosis following administration of transfer factor 总被引:8,自引:0,他引:8
Three patients with progressive coccidioidomycosis were given preparations of transfer factor (TF). Adverse reactions to TF were minimal. Following TF administration two of these patients had prolonged clinical remissions in their coccidioidal disease. Cellular immune responses were sequentially evaluated by coccidioidininduced delayed-type skin tests, lymphocyte blast transformation and macrophage inhibition factor production (MIF). These three patients each exhibited different cellular immune patterns before and after TF administration. Two patients converted their coccidioidin skin tests, and one converted lymphocyte transformation response to coccidioidin. Also, TF apparently favorably affected the MIF response in all three patients. 相似文献
6.
张伊璜 《微生物学免疫学进展》1994,22(2):49-52
目前,世界各国医学界均在积极探索非甲非乙型肝炎病毒的病原。随着分子克隆技术及特异性丙肝病毒抗原的出现,使特异性丙肝检测手段迅速发展,各种类型的诊断试剂盒不断推出,并在敏感性和待异性方面均有明显提高,日趋发展为简便、快速、可靠的方法。本文特就有关丙肝分子生物学及实验诊断技术的研究进展作一综述。 相似文献
7.
Malcolm J. Thompson Samson R. Dutky Yolanda Lehner Lonnie N. Standifier Elton W. Herbert 《Phytochemistry》1978,17(6):1053-1056
The esterified and unesterified sterol fractions of bee-gathered mixed pollens were examined, and total sterol composition was determined. Two new sterols of pollens, 14α-methyl-9β,19-cyclo-5α-cholest-24-en-3β-ol (24-dehydropollinastanol) and 14α-methyl-5α-ergost-24(28)-en-3β-ol (24-methylenepollinastanol) were isolated and identified. Both sterols were found primarily in the esterified sterol fraction, and 24-methylenepollinastanol accounted for 43% of the sterols of this fraction. 24-Dehydropollinastanol and four other sterols which also contain a 9β,19-cyclopropane ring were found only in the esterified sterol fraction. 24-Methylenecholesterol was the major sterol of the unesterified sterol fraction. 相似文献
8.
From dried leaves of Panax pseudo-ginseng subsp. himalaicus collected in Eastern Himalaya, new dammarane saponins, named pseudo-ginsenosides-F11 and -F8 were isolated along with the known Ginseng-root saponins, ginsenosides-Rb3, Rd and -Re. Pseudo-ginsenoside-F8 was proved to be a mono-acetyl-ginsenoside-Rb3 and the location of its acetyl group was established mainly by 13C NMR spectroscopy. Pseudo-ginsenoside-F11, was identified as the 6-O-α-rhamnopyransyl(1 → 2)-β-glucopyranoside of 3β,6α,12β,25-tetrahydoxy-(20S,24R)-epoxy-dammarane. The C-24 configuration of ocotillone and its related triterpenes was confirmed to be 24R excluding the recent comment by Lavie et al. 相似文献
9.
The structures of two 4α-methylsterols is isolated from Cucumis sativus(Cucurbitaceae) seeds were determined based mainly on their 13CNMR spectra as 24β-ethyl-31-norlanosta-8,25(27)-dien-3β-ol and 24β-ethyl-25(27)- dehydrolophenol, respectively, of which the former is a new sterol from natural sources. These two 4α-methylsterols were identified in the seeds of two other Cucurbitaceae species, Lagenaria leucantha var. Gourda and Citrullus battich. The probable biogenetic significance of the two 4α-methylsterols is discussed. Other 4α-methylsterols identified in the seeds of the three Cucurbitaceae species were obtusifoliol, cycloeucalenol and gramisterol. 相似文献
10.
Lanosterol and cycloartenol labelled with tritium at C-2, and 24-methylenecholesterol and fucosterol labelled with tritium at C-2 and C-4 were fed to actively growing cultures of Chlorella ellipsoidea. Lanosterol and cycloartenol were converted to each of the five desmethyl sterols of C. ellipsoidea. Lanosterol was more efficiently incorporated than cycloartenol.Although there was some evidence for the reduction of the 24-methylene group, it was apparent that 24-methylene-cholesterol was converted primarily to the C29 sterols, clionasterol and poriferasterol. Labelled fucosterol was reduced at the 24(28) double bond, producing clionasterol. 相似文献