全文获取类型
收费全文 | 16037篇 |
免费 | 2606篇 |
国内免费 | 1728篇 |
专业分类
化学 | 8101篇 |
晶体学 | 166篇 |
力学 | 828篇 |
综合类 | 106篇 |
数学 | 1254篇 |
物理学 | 4946篇 |
无线电 | 4970篇 |
出版年
2024年 | 74篇 |
2023年 | 465篇 |
2022年 | 583篇 |
2021年 | 772篇 |
2020年 | 656篇 |
2019年 | 631篇 |
2018年 | 546篇 |
2017年 | 524篇 |
2016年 | 747篇 |
2015年 | 780篇 |
2014年 | 904篇 |
2013年 | 1123篇 |
2012年 | 1353篇 |
2011年 | 1310篇 |
2010年 | 1004篇 |
2009年 | 990篇 |
2008年 | 973篇 |
2007年 | 884篇 |
2006年 | 875篇 |
2005年 | 767篇 |
2004年 | 488篇 |
2003年 | 430篇 |
2002年 | 424篇 |
2001年 | 312篇 |
2000年 | 298篇 |
1999年 | 320篇 |
1998年 | 278篇 |
1997年 | 269篇 |
1996年 | 274篇 |
1995年 | 226篇 |
1994年 | 197篇 |
1993年 | 134篇 |
1992年 | 128篇 |
1991年 | 112篇 |
1990年 | 104篇 |
1989年 | 85篇 |
1988年 | 68篇 |
1987年 | 33篇 |
1986年 | 50篇 |
1985年 | 32篇 |
1984年 | 22篇 |
1983年 | 20篇 |
1982年 | 17篇 |
1981年 | 8篇 |
1980年 | 11篇 |
1975年 | 8篇 |
1973年 | 5篇 |
1972年 | 7篇 |
1965年 | 6篇 |
1964年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Wenxue Li Jun Wen Jingyu He Di Cao Fanlu Sun Jinying Li Guorong Fan 《Journal of separation science》2013,36(19):3184-3190
A simple, rapid, high‐throughput, and highly sensitive LC–MS/MS was developed to determine anisodamine in a small volume (50 μL) of beagle dog plasma using atropine sulfate as the internal standard. The analyte and internal standard were isolated from 50 μL plasma samples after a one‐step protein precipitation using Sirocco 96‐well protein precipitation filtration plates. The separation was accomplished on a Hanbon Hedera CN column (100 × 4.6 mm, 5 μm) and the run time was 4 min. A Micromass Quatro Ultima mass spectrometer equipped with an ESI source was operated in the multiple reaction monitoring mode with the precursor‐to‐product ion transitions m/z 306.0→140.0 (anisodamine) and 290.0→123.9 (atropine) used for quantitation. The method was sensitive with a low LOQ of 0.05 ng/mL, and good linearity in the range 0.05–50 ng/mL for anisodamine (r2 ≥ 0.995). All the validation data, such as accuracy, intra‐ and interrun precision, were within the required limits. The method was successfully applied to the pharmacokinetic study of anisodamine hydrochloride injection in beagle dogs. 相似文献
72.
A practical protocol was disclosed for the nickel-catalyzed C-alkylation of 9-fluorenone hydrazone with alcohols using t-BuOK as the base, and 9-monoalkylated fluorene derivatives were obtained in good yields under the benign conditions. 相似文献
73.
In the presence of 1,8-diazabicycolo[5.4.0]undec-7-ene (DBU) and concentrated H2SO4, 2-naphthol reacted smoothly with α,β-unsaturated trifluoromethyl ketones in CH2Cl2 at room temperature, affording the 3-trifluoromethyl-substituted benzo[f]chromene derivatives in good to excellent yields in a one-pot reaction. [Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications® for the following free supplemental resource: Full experimental and spectral details]. 相似文献
74.
The C1–8 fragment of autolytimycin was synthesized via a reliable 10-step route capable of delivering 41% overall yield at multi-gram scale. As a key step, a chelation-controlled isopropenylation of α-oxygenated aldehydes was established with a reagent combination of diisopropenylzinc, magnesium halide, and a dichloromethane/toluene mixed solvent. Cram-chelate isopropenylation products dominated for aldehydes with a small α-substituents, such as –OMe and –OBn groups, while the Felkin product could be obtained with a bulky –OTBS group. 相似文献
75.
AbstractA convenient and efficient procedure for the synthesis of 2-substituted-6,7-dihydrobenzo[d]oxazol-4(5H)-ones and 2-aryl-6,7-dihydrobenzofuran-4(5H)-ones through a Rh2(OAc)4-catalyzed C≡X (X?=?N, C) insertion of cyclic 2-diazo-1,3-diketones with nitriles and aromatic alkynes has been developed. This reaction uses readily available starting materials and stable cyclic 2-diazo-1,3-diketone compounds, with desired products formed in good to high yields. A tentative mechanism involving a C≡X bond insertion and 1,5-dipolar electrocyclization/ring opening and cyclization sequence for this reaction is proposed. 相似文献
76.
Dr. Meiling Guo Prof. Dr. Zhaochi Feng Dr. Jan P. Hofmann Prof. Dr. Bert M. Weckhuysen Dr. Fengtao Fan Prof. Dr. Can Li 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(42):14200-14204
Microporous vanadosilicates with octahedral VO6 and tetrahedral SiO4 units, better known as AM‐6, have been hydrothermally synthesized with different morphologies by controlling the Na/K molar ratio of the initial gel mixtures. The morphology of the AM‐6 materials changed from bulky cube to nanofiber aggregates as the Na/K molar ratio decreased from 1.9 to 0.2. Raman spectroscopy revealed that the VO3? intermediate species plays an important role in the formation of the nanofiber morphology. The orientation of ‐V‐O‐V‐ chains in nanofiber aggregates was examined by confocal polarized micro‐Raman spectroscopy. It was found that these aggregates are assemblies of short ‐V‐O‐V‐ chains perpendicular to the axis of nanofibers. The obtained AM‐6 nanofibers greatly increase the exposed proportion of V? O terminals, and thus improve the catalytic performance. 相似文献
77.
In 1991,Hornik proved that the collection of single hidden layer feedforward neural networks(SLFNs)with continuous,bounded,and non-constant activation functionσis dense in C(K)where K is a compact set in R~s(see Neural Networks,4(2),251-257(1991)).Meanwhile,he pointed out"Whether or not the continuity assumption can entirely be dropped is still an open quite challenging problem".This paper replies in the affirmative to the problem and proves that for bounded and continuous almost everywhere(a.e.)activation functionσon R,the collection of SLFNs is dense in C(K)if and only ifσis un-constant a.e.. 相似文献
78.
Chuang Zhang Pingyi Fan Yunquan Dong Ke Xiong 《Wireless Communications and Mobile Computing》2015,15(13):1681-1694
To provide stable and high data rate wireless access for passengers in the train, it is necessary to properly deploy base stations along the railway. We consider this issue from the perspective of service, which is defined as the integral of the time‐varying instantaneous channel capacity. With large‐scale fading assumption, it will be shown that the total service of each base station is inversely proportional to the velocity of the train. Besides, we find that if the ratio of the service provided by a base station in its service region to its total service is given, the base station interval (i.e., the distance between two adjacent base stations) is a constant regardless of the velocity of the train. On the other hand, if a certain amount of service is required, the interval will increase with the velocity of the train. The aforementioned results apply not only to simple curve rails, like line rail and arc rail, but also to any irregular curve rail, provided that the train is traveling at a constant velocity. Furthermore, the new developed results are applied to analyze the on–off transmission strategy of base stations. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
79.
Kuan-Yu Lin Chak Hin Lam Xin-Hui Lin Jung-I Hsu Syuan-Yun Fan Dr. Nitesh K. Gupta Yu-Chun Lin Boon Khoon Tee Jui-Ping Li Dr. Jen-Kun Chen Prof. Dr. Kui-Thong Tan 《化学:亚洲杂志》2021,16(8):937-948
To date, various affinity-based protein labeling probes have been developed and applied in biological research to modify endogenous proteins in cell lysates and on the cell surface. However, the reactive groups on the labeling probes are also the cause of probe instability and nonselective labeling in a more complex environment, e. g., intracellular and in vivo. Here, we show that labeling probes composed of a sterically stabilized difluorophenyl pivalate can achieve efficient and selective labeling of endogenous proteins on the cell surface, inside living cells and in vivo. As compared with the existing protein labeling probes, probes with the difluorophenyl pivalate exhibit several advantages, including long-term stability in stock solutions, resistance to enzymatic hydrolysis and can be customized easily with diverse fluorophores and protein ligands. With this probe design, endogenous hypoxia biomarker in living cells and nude mice were successfully labeled and validated by in vivo, ex vivo, and immunohistochemistry imaging. 相似文献
80.
Saijie Wang Zhijian Liu Sen Wu Hongyan Sun Wu Zeng Jintao Wei Zixiao Fan Zhuohang Sui Liankun Liu Xinxiang Pan 《Electrophoresis》2021,42(21-22):2223-2229
To improve the accuracy and efficiency of ships’ ballast water detection, the separation of microalgae according to size is significant. In this article, a method to separate microalgae based on inertia-enhanced pinched flow fractionation (iPFF) was reported. The method utilized the inertial lift force induced by flow to separate microalgae according to size continuously. The experimental results show that, as the Reynolds number increases, the separation effect becomes better at first, but then stays unchanged. The best separation effect can be obtained when the Reynolds number is 12.3. In addition, with the increase of the flow rate ratio between sheath fluid and microalgae mixture, the separation effect becomes better and the best separation effect can be obtained when the flow rate ratio reaches 10. In this case, the recovery rate of Tetraselmis sp. is about 90%, and the purity is about 86%; the recovery rate of Chlorella sp. is as high as 99%, and the purity is about 99%. After that, the separation effect keeps getting better but very slowly. In general, this study provides a simple method for the separation of microalgae with different sizes, and lays a foundation for the accurate detection of microalgae in the ballast water. 相似文献