全文获取类型
收费全文 | 6372篇 |
免费 | 1018篇 |
国内免费 | 3716篇 |
出版年
2024年 | 87篇 |
2023年 | 250篇 |
2022年 | 355篇 |
2021年 | 399篇 |
2020年 | 403篇 |
2019年 | 432篇 |
2018年 | 258篇 |
2017年 | 281篇 |
2016年 | 284篇 |
2015年 | 406篇 |
2014年 | 604篇 |
2013年 | 500篇 |
2012年 | 708篇 |
2011年 | 651篇 |
2010年 | 563篇 |
2009年 | 569篇 |
2008年 | 610篇 |
2007年 | 596篇 |
2006年 | 520篇 |
2005年 | 456篇 |
2004年 | 337篇 |
2003年 | 293篇 |
2002年 | 232篇 |
2001年 | 229篇 |
2000年 | 233篇 |
1999年 | 163篇 |
1998年 | 89篇 |
1997年 | 73篇 |
1996年 | 37篇 |
1995年 | 38篇 |
1994年 | 21篇 |
1993年 | 24篇 |
1992年 | 22篇 |
1991年 | 31篇 |
1990年 | 31篇 |
1989年 | 46篇 |
1988年 | 21篇 |
1987年 | 15篇 |
1986年 | 35篇 |
1985年 | 13篇 |
1984年 | 18篇 |
1983年 | 18篇 |
1982年 | 23篇 |
1981年 | 11篇 |
1979年 | 8篇 |
1978年 | 8篇 |
1977年 | 6篇 |
1976年 | 9篇 |
1967年 | 9篇 |
1965年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
91.
To investigate the biological characterization and antitumor activitites of GM-CSF gene-transfected dendritic cells, the splenic dendritic cells were infected with GM-CSF recombinant replication-deficient adenoviruses in vitro . Their enhanced expression of B7 was demonstrated by FACS analysis, and more potent stimulatory activity was confirmed by allogeneic MLR. Immunization of dendritic cells pulsed with irradiated B16 melanoma cells induced sig-nificant CTL and enabled host to resist the challenge of wild-type B16 cells. When they were transfected with GM-CSF gene subsequently, the induced CTL activity was higher, and the produced protection against B16 cell challenge and therapeutic effect on the mice with preestablished pulmonary melastases more effective. These data suggest that the dendritic cells pulsed with tumor antigen then transfected with GM-CSF gene can be used as an effective vaccine in tumor immunotherapy. 相似文献
92.
马尾松毛虫雄蛾触角毛状感受器的细微结构 总被引:6,自引:0,他引:6
马尾松毛虫Dendrolimus punctagus(Walker)雄蛾有一对羽毛状触角。在触角鞭节的每对侧枝的内侧(迎风面)着生许多毛状感受器。每个毛状感受器由几丁质表皮毛及位于其下的三个感觉神经原和三个呈同心排列的辅助细胞-鞘原细胞、毛原细胞和膜原细胞构成。几丁质表皮毛上有许多孔。毛腔内充满感受器淋巴液。感觉神经原发出的树状突伸入毛腔,浸浴于感受器淋巴液内。这些结构特征表明它是一种司嗅觉的化学感受器。雄蛾终生不取食,推断它的嗅觉感受器主要用以感受雌蛾释放的性外激素,帮助寻找配偶。 相似文献
93.
四川省鱼类寄生粘孢子虫两新种(粘孢子纲:双壳目) 总被引:1,自引:0,他引:1
本四川省鱼类寄生粘孢子虫两新种:寄生墨头鱼的宜宾两极虫,新种Myxidium yibinense sp.nov.和寄生鳙Aristichthys nkbilis的鳙单尾虫,新种Unicauda aristichthydis sp.nov。 相似文献
94.
95.
含单核中后期至后期花粉的蚕豆离体花药,经过2mM丁酸钠24小时预处理后,再漂浮培养于pH5.8或7.0的液体培养基。以不经预处理的作为对照。结果如下: 1.培养后9天内,丁酸钠预处理和培养基pH值并不明显影响花粉退化百分率。2.培养初期,pH7.0显著促进小孢子不等分裂。3.丁酸钠预处理抑制培养初期的小孢子有丝分裂,而后又显著增加小孢子均等分裂百分率。4.丁酸钠预处理导致小孢子有丝分裂类型的趋向改变。本文还对丁酸钠导致有丝分裂类型趋向改变的可能原因,进行了讨论。 相似文献
96.
Electron transport has been studied by flash absorption and EPR spectroscopies at 10–30 K in Photosystem I particles prepared with digitonin under different redox conditions. In the presence of ascorbate, an irreversible charge separation is progressively induced at 10 K between P-700 and iron-sulfur center A by successive laser flashes, up to a maximum which corresponds to about two-thirds of the reaction centers. In these centers, heterogeneity of the rate for center A reduction is also shown. In the other third of reaction centers, the charge separation is reversible and relaxes with a t1/2 ≈ 120 μs. When the iron-sulfur centers A and B are prereduced, the 120 μs relaxation becomes the dominant process (70–80% of the reaction centers), while a slow component (t1/2 = 50–400 ms) reflecting the recombination between P-700+ and center X− occurs in a minority of reaction centers (10–15%). Flash absorption and EPR experiments show that the partner of P-700+ in the 120 μs recombination is neither X nor a chlorophyll but more probably the acceptor A−1 as defined by Bonnerjea and Evans (Bonnerjea, J. and Evans, M.C.W. (1982) FEBS Lett. 148, 313–316). The role of center X in low-temperature electron flow is also discussed. 相似文献
97.
98.
99.
在不同生境的松林中,人工补充寄主卵都能提高寄生效果。但林地生境不同,寄生率有明显差异。在松阔混交林中补充寄主,其寄生率比对照提高5.5—16.2倍。植被稀疏的纯松林效果较差,补充的寄生率比对照提高3.0倍。 卵蜂种群消长随季节温度而变化,全年以5月中旬至6月下旬和9月中旬至10月中旬为两个寄生高峰。卵蜂种群与松毛虫种群的消长存在较明显的相依关系,卵蜂种群随着松毛虫种群的消长而消长。施药对卵蜂种群有较大影响,施药区比对照区的寄生率约降低一倍。在混交林中填充寄主卵,能促进卵蜂种群世代延续。在逐步改善林地生境的基础上,利用人工补充寄主,可以代替人工繁蜂放蜂。 相似文献
100.
The formation of the triplet state of carotenoids (detected by an absorption peak at 515 nm) and the photo-oxidation of the primary donor of Photosystem II, P-680 (detected by an absorption increase at 820 nm) have been measured by flash absorption spectroscopy in chloroplasts in which the oxygen evolution was inhibited by treatment with Tris. The amount of each transient form has been followed versus excitation flash intensity (at 590 or 694 nm). At low excitation energy the quantum yield of triplet formation (with the Photosystem II reaction center in the state Q−) is about 30% that of P-680 photo-oxidation. The yield of carotenoid triplet formation is higher in the state Q− than in the state Q, in nearly the same proportion as chlorophyll a fluorescence. It is concluded that, for excited chlorophyll a, the relative rates of intersystem crossing to the triplet state and of fluorescence emission are the same in vivo as in organic solvent. At high flash intensity the signal of P-680+ completely saturates, whereas that of carotenoid triplet continues to increase.
The rate of triplet-triplet energy transfer from chlorophyll a to carotenoids has been derived from the rise time of the absorption change at 515 nm, in chloroplasts and in several light-harvesting pigment-protein complexes. In all cases the rate is very high, around 8 · 107 s−1 at 294 K. It is about 2–3 times slower at 5 K. The transitory formation of chlorophyll triplet has been verified in two pigment-protein complexes, at 5 K. 相似文献