全文获取类型
收费全文 | 3951篇 |
免费 | 166篇 |
国内免费 | 237篇 |
专业分类
系统科学 | 190篇 |
丛书文集 | 130篇 |
教育与普及 | 58篇 |
理论与方法论 | 27篇 |
现状及发展 | 68篇 |
研究方法 | 38篇 |
综合类 | 3829篇 |
自然研究 | 14篇 |
出版年
2024年 | 7篇 |
2023年 | 24篇 |
2022年 | 55篇 |
2021年 | 77篇 |
2020年 | 84篇 |
2019年 | 50篇 |
2018年 | 54篇 |
2017年 | 73篇 |
2016年 | 81篇 |
2015年 | 154篇 |
2014年 | 231篇 |
2013年 | 281篇 |
2012年 | 334篇 |
2011年 | 351篇 |
2010年 | 319篇 |
2009年 | 353篇 |
2008年 | 348篇 |
2007年 | 358篇 |
2006年 | 288篇 |
2005年 | 232篇 |
2004年 | 139篇 |
2003年 | 88篇 |
2002年 | 98篇 |
2001年 | 74篇 |
2000年 | 59篇 |
1999年 | 45篇 |
1998年 | 13篇 |
1997年 | 26篇 |
1996年 | 11篇 |
1995年 | 9篇 |
1994年 | 5篇 |
1993年 | 4篇 |
1992年 | 2篇 |
1991年 | 6篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1986年 | 2篇 |
1982年 | 1篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1976年 | 2篇 |
1972年 | 2篇 |
1971年 | 2篇 |
排序方式: 共有4354条查询结果,搜索用时 15 毫秒
41.
藻胆蛋白表达条件优化的研究 总被引:1,自引:0,他引:1
为了提高藻胆蛋白的表达含量,对本实验室构建的含pACYCDuet-ho1-pcyA、pETDuet-pecE-pecF、pCO-LADuet-pecA的E.coliBL21菌种的表达条件进行优化。通过单因素实验和正交实验L9(33)优化了蛋白的表达条件为:诱导表达温度为28℃,诱导表达时间为14h,诱导剂量为1.0mmol/L,藻胆蛋白最高表达含量为11.271mg/100mL. 相似文献
42.
针对无机化学授课对象多而广,所需试剂种类及用量庞大,产生的废气、废液、废渣等对环境具有危害的特点,通过整合优化实验内容,规范实验操作,采用微型实验、多媒体及网上虚拟实验室,合理收集及处理三废等方面的改革创新.将绿色化学的理念深入到无机化学实验的各个环节中,以初步实现无机化学实验教学的“绿色化”,培养学生的绿色意识. 相似文献
43.
通过FT-IR和DSC等研究了L iC l对脂肪族聚氨酯脲溶液粘度以及聚氨酯脲膜的结构和性能的影响。研究结果表明:L iC l的加入使聚氨酯脲溶液的初期粘度降低,后期粘度升高;含L iC l的聚氨酯脲的Tg和氨酯羰基的氢键化程度提高,但脲羰基的氢键化程度降低;L iC l的加入使聚氨酯脲的拉伸模量、硬度、撕裂强度和吸水率显著升高。 相似文献
44.
Regulation of primary cilia formation and left-right patterning in zebrafish by a noncanonical Wnt signaling mediator, duboraya 总被引:1,自引:0,他引:1
Oishi I Kawakami Y Raya A Callol-Massot C Izpisúa Belmonte JC 《Nature genetics》2006,38(11):1316-1322
Primary cilia are microtubule-based organelles that project from the surface of nearly every animal cell. Although important functions of primary cilia in morphogenesis and tissue homeostasis have been identified, the mechanisms that control the formation of primary cilia are not understood. Here we characterize a zebrafish gene, termed duboraya (dub), that is essential for ciliogenesis. Knockdown of dub in zebrafish embryos results in both defects in primary cilia formation in Kupffer's vesicle and randomization of left-right organ asymmetries. We show that, at the molecular level, the function of dub in ciliogenesis is regulated by phosphorylation, which in turn depends on Frizzled-2-mediated noncanonical Wnt signaling. We also provide evidence that, at the cellular level, dub function is essential for actin organization in the cells lining Kupffer's vesicle. Taken together, our findings identify a molecular factor that links noncanonical Wnt signaling with the control of left-right axis specification, and provide an entry point for analyzing the mechanisms that regulate primary cilia formation. 相似文献
45.
Florian Hoss Juan F. Rodriguez-Alcazar Eicke Latz 《Cellular and molecular life sciences : CMLS》2017,74(7):1211-1229
The inflammasome adapter ASC links activated inflammasome sensors to the effector molecule pro-caspase-1. Recruitment of pro-caspase-1 to ASC promotes the autocatalytic activation of caspase-1, which leads to the release of pro-inflammatory cytokines, such as IL-1β. Upon triggering of inflammasome sensors, ASC assembles into large helical fibrils that interact with each other serving as a supramolecular signaling platform termed the ASC speck. Alternative splicing, post-translational modifications of ASC, as well as interaction with other proteins can perturb ASC function. In several inflammatory diseases, ASC specks can be found in the extracellular space and its presence correlates with poor prognosis. Here, we review the role of ASC in inflammation, and focus on the structural mechanisms that lead to ASC speck formation, the regulation of ASC function during inflammasome assembly, and the importance of ASC specks in disease. 相似文献
46.
Lorena Beatriz Quiroga María Daniela Moreno Ariel Aníbal Cataldo Juan Héctor Aragón-Traverso María Victoria Pantano Juan Pablo Segundo Olivares 《Journal of Natural History》2015,49(27-28):1703-1716
The American bullfrog Lithobates catesbeianus has been introduced around the world, with invasive populations reported from almost all South American countries. A population of this species was introduced in the Calingasta department of San Juan province, which is an arid environment in western Argentina. This work provides information on the dietary composition of an invasive population of L. catesbeianus, and compares the degree of dietary overlap between adults and juveniles. Stomach contents of 169 bullfrogs (82 adults and 87 juveniles) were analysed. Adults consumed 40 prey taxa and Hymenoptera (Insecta) was the most numerous prey item (41.8%), followed by Araneae (13.6%) and Aeglidae (13.4%). Juveniles consumed 29 prey taxa and Hymenoptera constituted the highest percentage in prey number (77.2%). The trophic overlap niche index at the same level shows a value of 0.64 overlap in dietary community between adults and juveniles of this bullfrog. Aeglidae was volumetrically the most important trophic item (25.4%), followed by Anura (25.02%). Our results showed that cannibalism in bullfrogs is more common than the consumption of native anurans, coinciding with that reported in other populations of introduced bullfrogs. The high similarity in the diets of both size classes and the association between the size of the predator and prey suggest that the impact caused by bullfrogs throughout their ontogeny is high and probably has an impact on their prey. Freshwater crabs are the main items in the diet of Lithobates catesbeianus in other introduced populations and are usually the most conspicuous at our study site. The crabs in freshwater ecosystems are part of the lowest trophic level in the food chain. The major threats to the southern region’s freshwater crabs include deforestation, farming and exotic species. Lithobates catesbeianus has a generalist diet and high overlap between adults and juveniles. 相似文献
47.
We introduce a new strategy for the prediction of linear temporal aggregates; we call it ‘hybrid’ and study its performance using asymptotic theory. This scheme consists of carrying out model parameter estimation with data sampled at the highest available frequency and the subsequent prediction with data and models aggregated according to the forecasting horizon of interest. We develop explicit expressions that approximately quantify the mean square forecasting errors associated with the different prediction schemes and that take into account the estimation error component. These approximate estimates indicate that the hybrid forecasting scheme tends to outperform the so‐called ‘all‐aggregated’ approach and, in some instances, the ‘all‐disaggregated’ strategy that is known to be optimal when model selection and estimation errors are neglected. Unlike other related approximate formulas existing in the literature, those proposed in this paper are totally explicit and require neither assumptions on the second‐order stationarity of the sample nor Monte Carlo simulations for their evaluation. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
48.
Lin Z Bei JX Shen M Li Q Liao Z Zhang Y Lv Q Wei Q Low HQ Guo YM Cao S Yang M Hu Z Xu M Wang X Wei Y Li L Li C Li T Huang J Pan Y Jin O Wu Y Wu J Guo Z He P Hu S Wu H Song H Zhan F Liu S Gao G Liu Z Li Y Xiao C Li J Ye Z He W Liu D Shen L Huang A Wu H Tao Y Pan X Yu B Tai ES Zeng YX Ren EC Shen Y Liu J Gu J 《Nature genetics》2012,44(1):73-77
To identify susceptibility loci for ankylosing spondylitis, we performed a two-stage genome-wide association study in Han Chinese. In the discovery stage, we analyzed 1,356,350 autosomal SNPs in 1,837 individuals with ankylosing spondylitis and 4,231 controls; in the validation stage, we analyzed 30 suggestive SNPs in an additional 2,100 affected individuals and 3,496 controls. We identified two new susceptibility loci between EDIL3 and HAPLN1 at 5q14.3 (rs4552569; P = 8.77 × 10(-10)) and within ANO6 at 12q12 (rs17095830; P = 1.63 × 10(-8)). We also confirmed previously reported associations in Europeans within the major histocompatibility complex (MHC) region (top SNP, rs13202464; P < 5 × 10(-324)) and at 2p15 (rs10865331; P = 1.98 × 10(-8)). We show that rs13202464 within the MHC region mainly represents the risk effect of HLA-B*27 variants (including HLA-B*2704, HLA-B*2705 and HLA-B*2715) in Chinese. The two newly discovered loci implicate genes related to bone formation and cartilage development, suggesting their potential involvement in the etiology of ankylosing spondylitis. 相似文献
49.
利用高效液相色谱法建立牛黄解毒制剂中胆红素的含量测定方法,色谱柱为Agilent Zorbax SB-C18色谱柱,流动相为乙腈—1%冰醋酸(95∶5),检测波长为450 nm.结果显示,胆红素进样量在0.8321~208.032 ng范围内具有良好的线性关系,r=0.9995,牛黄解毒片平均回收率为105.6%,RSD为1.42%,牛黄解毒丸平均回收率为96.2%,RSD为1.83%.结果表明,方法准确、简便,可作为牛黄解毒片及牛黄解毒丸等制剂中胆红素含量的测定方法. 相似文献
50.
目的探讨3.0 T磁敏感加权成像在颅内胶质瘤诊断中的应用价值.方法经手术病理证实的20例高级别胶质瘤和12例低级别胶质瘤,均行MRI扫描和SWI,15例(10例高级别胶质瘤和5例低级别胶质瘤)于增强前后行SWI.将SWI与常规T1 FLAIR、T1 FLAIR增强图像作比较,并对SWI瘤内低信号形态及数量进行分级评分.... 相似文献