全文获取类型
收费全文 | 39030篇 |
免费 | 3124篇 |
国内免费 | 3198篇 |
专业分类
45352篇 |
出版年
2024年 | 102篇 |
2023年 | 588篇 |
2022年 | 1395篇 |
2021年 | 2193篇 |
2020年 | 1416篇 |
2019年 | 1793篇 |
2018年 | 1695篇 |
2017年 | 1184篇 |
2016年 | 1642篇 |
2015年 | 2417篇 |
2014年 | 2882篇 |
2013年 | 3146篇 |
2012年 | 3610篇 |
2011年 | 3246篇 |
2010年 | 1918篇 |
2009年 | 1719篇 |
2008年 | 2012篇 |
2007年 | 1731篇 |
2006年 | 1522篇 |
2005年 | 1251篇 |
2004年 | 1036篇 |
2003年 | 865篇 |
2002年 | 744篇 |
2001年 | 662篇 |
2000年 | 576篇 |
1999年 | 619篇 |
1998年 | 354篇 |
1997年 | 383篇 |
1996年 | 349篇 |
1995年 | 333篇 |
1994年 | 301篇 |
1993年 | 223篇 |
1992年 | 322篇 |
1991年 | 225篇 |
1990年 | 192篇 |
1989年 | 181篇 |
1988年 | 115篇 |
1987年 | 100篇 |
1986年 | 85篇 |
1985年 | 86篇 |
1984年 | 37篇 |
1983年 | 42篇 |
1982年 | 21篇 |
1981年 | 16篇 |
1980年 | 13篇 |
1979年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Cheng Jianxin Xia Yuqing Zhou Cheng Li Xiaohao Liu Pengfei 《Marine biotechnology (New York, N.Y.)》2023,25(2):291-313
Marine Biotechnology - Takifugu rubripes is important commercially fish species in China and it is under serious threat from white spot disease (cyptocaryoniasis), which leads to heavy economic... 相似文献
22.
广西、云南的PSEUDOSCHWAGERINA化石及其地层意义 总被引:8,自引:4,他引:4
该文记述了广西宜山马脑山剖面及云南八宝小独山剖面Pseudoschwaserina属34种(亚种),分析了两剖面Pseudoschwagerina动物群的面貌,讨论了Pseudoschwagerina的地层意义。研究表明,两剖面Pseudoschwagerina动物群具有地方性种稀少的共同特点,大多数种皆为广相型分子。从动物群的组成上看,广西、云南Pseudoschwagerina动物群与我国贵州、北美及俄罗斯等地的Pseudoschwagerina动物群有较大的相似性。但是,目前归入 Pseudoschwagerina名下的各种在形态上有着较大的差异,造成不同地区合Pseudoschwagerina地层带化石难以直接对比。根据对两剖面Pseudoschwagerina地层分布规律的研究以及国内、外Pseudochwagerina地理分布的资料,笔者建议选用 Pseudoschwagerina uddeni,P.beedei,P.robusta等 Pseudoschwagerina的典型分子做为含Pseudoschwagerina地层划分、对比的首要标准类群,选用P.uddeni和P.robusta分别做为确定Pseudoschwagerina带底、顶界线的首要标准种,以便于含Pseudoschwagerina地层的全球性的对比。 相似文献
23.
Wang Zunxin Wang Xianyu Liu Siqin Yang Ying Li Yang Chen Siyuan Wang Guangpeng Zhang Xincheng Ye Yuxiu Hu Laibao Zhou Qing Wang Feibing Chen Xinhong 《Journal of Plant Growth Regulation》2023,42(1):294-303
Journal of Plant Growth Regulation - Zinc is an important micronutrient for the growth and development of human body and plants. Proper use of nitrogen fertilizer and foliar application of Zn have... 相似文献
24.
James Kang William Low Thomas Norberg Jill Meisenhelder Karin Hansson Johan Stenflo Guo-Ping Zhou Julita Imperial Baldomero M Olivera Alan C Rigby A Grey Craig 《European journal of biochemistry》2004,271(23-24):4939-4949
The 13-amino acid glycopeptide tx5a (Gla-Cys-Cys-Gla-Asp-Gly-Trp*-Cys-Cys-Thr*-Ala-Ala-Hyp-OH, where Trp* = 6-bromotryptophan and Thr* = Gal-GalNAc-threonine), isolated from Conus textile, causes hyperactivity and spasticity when injected intracerebral ventricularly into mice. It contains nine post-translationally modified residues: four cysteine residues, two gamma-carboxyglutamic acid residues, and one residue each of 6-bromotryptophan, 4-trans-hydroxyproline and glycosylated threonine. The chemical nature of each of these has been determined with the exception of the glycan linkage pattern on threonine and the stereochemistry of the 6-bromotryptophan residue. Previous investigations have demonstrated that tx5a contains a disaccharide composed of N-acetylgalactosamine (GalNAc) and galactose (Gal), but the interresidue linkage was not characterized. We hypothesized that tx5a contained the T-antigen, beta-D-Gal-(1-->3)-alpha-D-GalNAc, one of the most common O-linked glycan structures, identified previously in another Conus glycopeptide, contalukin-G. We therefore utilized the peracetylated form of this glycan attached to Fmoc-threonine in an attempted synthesis. While the result-ing synthetic peptide (Gla-Cys-Cys-Gla-Asp-Gly-Trp*-Cys-Cys-Thr*-Ala-Ala-Hyp-OH, where Trp* =6-bromotryptophan and Thr* = beta-D-Gal-(1-->3)-alpha-D-GalNAc-threonine) and the native peptide had almost identical mass spectra, a comparison of their RP-HPLC chromatograms suggested that the two forms were not identical. Two-dimensional 1H homonuclear and 13C-1H heteronuclear NMR spectroscopy of native tx5a isolated from Conus textile was then used to determine that the glycan present on tx5a indeed is not the aforementioned T-antigen, but rather alpha-D-Gal-(1-->3)-alpha-D-GalNAc. 相似文献
25.
Morphometric Analysis of Hepatocellular carcinomaLaiMao-de(来茂德);ChenPei-hui(陈培辉)andZhouShui-yun(周水云)(DepartmentofPathology,Zh... 相似文献
26.
黄精凝集素Ⅱ分子稳定性与生物学活性研究鲍锦库,曾仲奎,周红(四川大学生物系,成都,610064)本文在黄精凝集素Ⅱ纯化及性质研究的基础上,应用多种变性条件,研究其分子特性,同时对分子的巯基和色氨酸进行修饰,研究该凝集素分子保持其生物学活性与这些基团的... 相似文献
27.
Qian Shi Pascal Verdier-Pinard Arnold Brossi Ernest Hamel Kuo-Hsiung Lee 《Bioorganic & medicinal chemistry》1997,5(12):2277-2282
(+)-Thiocolchicine (2b) was prepared from (±)-colchicine (1) in a five-step reaction sequence that included chromatographic separation of appropriate camphanylated diastereomers. Acid hydrolysis of the (+)-diastereomer, followed by acetylation, yielded the desired product 2b. (+)-Thiocolchicine has 15-fold lower inhibitory activity against tubulin polymerization than (−)-thiocolchicine, and is 29-fold less potent for inhibiting growth of human Burkitt lymphoma cells. The enantiomer 2a, prepared from the (−)-camphanylated diastereomer, had potent activity in all assays comparable to that of (−)-thiocolchicine prepared by other methods. These results support the hypothesis that the proper configuration of colchicine-related compounds is an important requirement for their anti-tubulin action. 相似文献
28.
Physiologic and yield effects of mixtalol at various concentrations sprayed on rape at the anthesis stage were examined. Foliar sprays of 4 and 2 ppm mixtalol significantly increased the chlorophyll content of rape leaves and pods, reduced the accumulation of malondialdehyde and ethylene production, and delayed the degradation of superoxide dismutase and catalase activities of the rape plant. Mixtalol also increased root oxidizability. Meanwhile, the number of branches and pods per plant was increased, and a 10.7% and 8.2% increase of seed yield over the controls was observed with treatments of 4 and 2 ppm mixtalol, respectively. No significant effects from mixtalol were observed on the maturation of plants or on the seed oil content or the erucic acid and glucosinolate content. Total rape oil production increased with 4 and 2 ppm mixtalol significantly by 12.4% and 10.5%, respectively, over the controls.Abbreviations MTL
mixtalol
- MDA
malondialdehyde
- TBA
thiobarbituric acid
- SOD
Superoxide dismutase
- CAT
catalase
- TTC
tetrazolium 相似文献
29.
R W Leu A Q Zhou M J Kennedy B J Shannon 《Journal of immunology (Baltimore, Md. : 1950)》1991,146(4):1233-1239
Studies originally designed to assess the putative role of endogenous C5 in macrophage activation for antibody-dependent cellular cytotoxicity (ADCC) yielded unanticipated results. Resident and inflammatory peritoneal macrophages from C5-deficient AKR mice were found to have significantly lower capacity for FcR-dependent ADCC activation and phagocytosis of IgG-opsonized SRBC targets than did C5-competent C3HeB/FeJ (C3H) mice. Reconstitution of the ADCC response of AKR macrophages was accomplished initially with C5-sufficient C3H mouse serum, which suggested that endogenous C5 may be required for ADCC activation. However, further investigation largely eliminated C5 involvement in that a heat-labile component of C5-deficient AKR serum was shown to be active in the reconstitution of ADCC activation of AKR macrophages. Macrophages from AKR mice were found to have significantly lower levels of C1q mRNA synthesis, endogenous C1q levels, and C1q secretion than did C3H mouse macrophages as determined by Northern blot, Western blot, and presynthetic radiolabeling analysis, respectively. The addition of purified exogenous C1q to IgG-opsonized SRBC targets fully reconstituted ADCC activation for AKR inflammatory peritoneal macrophages to levels of normally FcR-responsive C3H macrophages. Similarly, exogenous C1q augmented FcR-dependent phagocytosis of AKR macrophages but had no effect on macrophages from responsive C3H mice. Our results indicate that AKR mice have a deficiency for FcR-dependent cellular cytotoxicity and phagocytosis that is related to their low potential for C1q synthesis and secretion rather than to their established genetic deficiency for C5 synthesis. We tentatively conclude that endogenous C1q is required as an accessory molecule for macrophage FcR-dependent effector functions and that C5 is not a prerequisite for ADCC activation. 相似文献
30.