全文获取类型
收费全文 | 1114篇 |
免费 | 27篇 |
国内免费 | 9篇 |
专业分类
化学 | 671篇 |
晶体学 | 8篇 |
力学 | 79篇 |
数学 | 139篇 |
物理学 | 253篇 |
出版年
2022年 | 7篇 |
2021年 | 10篇 |
2020年 | 9篇 |
2019年 | 11篇 |
2018年 | 10篇 |
2017年 | 7篇 |
2016年 | 13篇 |
2015年 | 10篇 |
2014年 | 18篇 |
2013年 | 65篇 |
2012年 | 48篇 |
2011年 | 54篇 |
2010年 | 25篇 |
2009年 | 30篇 |
2008年 | 47篇 |
2007年 | 67篇 |
2006年 | 58篇 |
2005年 | 50篇 |
2004年 | 27篇 |
2003年 | 39篇 |
2002年 | 38篇 |
2001年 | 18篇 |
2000年 | 31篇 |
1999年 | 16篇 |
1998年 | 16篇 |
1997年 | 15篇 |
1996年 | 22篇 |
1995年 | 15篇 |
1994年 | 14篇 |
1993年 | 20篇 |
1992年 | 23篇 |
1991年 | 20篇 |
1990年 | 16篇 |
1989年 | 9篇 |
1988年 | 19篇 |
1987年 | 13篇 |
1986年 | 11篇 |
1985年 | 12篇 |
1983年 | 17篇 |
1981年 | 12篇 |
1980年 | 19篇 |
1979年 | 11篇 |
1978年 | 8篇 |
1977年 | 27篇 |
1976年 | 8篇 |
1975年 | 15篇 |
1974年 | 15篇 |
1973年 | 12篇 |
1972年 | 10篇 |
1968年 | 8篇 |
排序方式: 共有1150条查询结果,搜索用时 15 毫秒
211.
Jared B. Shaw Tzu-Yung Lin Franklin E. LeachIII Aleksey V. Tolmachev Nikola Tolić Errol W. Robinson David W. Koppenaal Ljiljana Paša-Tolić 《Journal of the American Society for Mass Spectrometry》2016,27(12):1929-1936
We provide the initial performance evaluation of a 21 Tesla Fourier transform ion cyclotron resonance mass spectrometer operating at the Environmental Molecular Sciences Laboratory at the Pacific Northwest National Laboratory. The spectrometer constructed for the 21T system employs a commercial dual linear ion trap mass spectrometer coupled to a FTICR spectrometer designed and built in-house. Performance gains from moving to higher magnetic field strength are exemplified by the measurement of peptide isotopic fine structure, complex natural organic matter mixtures, and large proteins. Accurate determination of isotopic fine structure was demonstrated for doubly charged Substance P with minimal spectral averaging, and 8158 molecular formulas assigned to Suwannee River Fulvic Acid standard with root-mean-square (RMS) error of 10 ppb. We also demonstrated superior performance for intact proteins; namely, broadband isotopic resolution of the entire charge state distribution of apo-transferrin (78 kDa) and facile isotopic resolution of monoclonal antibody under a variety of acquisition parameters (e.g., 6 s time-domains with absorption mode processing yielded resolution of approximately 1 M at m/z?=?2700). 相似文献
212.
213.
Lindorff-Larsen K Trbovic N Maragakis P Piana S Shaw DE 《Journal of the American Chemical Society》2012,134(8):3787-3791
The accurate characterization of the structure and dynamics of proteins in disordered states is a difficult problem at the frontier of structural biology whose solution promises to further our understanding of protein folding and intrinsically disordered proteins. Molecular dynamics (MD) simulations have added considerably to our understanding of folded proteins, but the accuracy with which the force fields used in such simulations can describe disordered proteins is unclear. In this work, using a modern force field, we performed a 200 μs unrestrained MD simulation of the acid-unfolded state of an experimentally well-characterized protein, ACBP, to explore the extent to which state-of-the-art simulation can describe the structural and dynamical features of a disordered protein. By comparing the simulation results with the results of NMR experiments, we demonstrate that the simulation successfully captures important aspects of both the local and global structure. Our simulation was ~2 orders of magnitude longer than those in previous studies of unfolded proteins, a length sufficient to observe repeated formation and breaking of helical structure, which we found to occur on a multimicrosecond time scale. We observed one structural feature that formed but did not break during the simulation, highlighting the difficulty in sampling disordered states. Overall, however, our simulation results are in reasonable agreement with the experimental data, demonstrating that MD simulations can already be useful in describing disordered proteins. Finally, our direct calculation of certain NMR observables from the simulation provides new insight into the general relationship between structural features of disordered proteins and experimental NMR relaxation properties. 相似文献
214.
Concise routes to five pharmacologically relevant bis-heterocyclic scaffolds are described. Significant molecular complexity is generated in a mere two synthetic operations enabling access to each scaffold. Routes are often improved by microwave irradiation and all utilize isocyanide-based multi-component reaction methods to incorporate the required diversity elements. Common reagents in all initial condensation reactions include 2-(N-Boc-amino)-phenyl-isocyanide 1, mono-Boc-phenylenediamine 2 and ethyl glyoxalate 3. 相似文献
215.
Three scaffolds of benzimidazoles, bis-benzimidazoles, and bis-benzimidazole-dihydroquinoxalines were synthesized via Ugi/de-protection/cyclization methodology. Benzimidazole forming ring
closure was enabled under microwave irradiation in the presence of 10% TFA/DCE. The methodology demonstrates the utility of
2-(N-Boc-amino)-phenyl-isocyanide for the generation of new molecular diversity. 相似文献
216.
A series of 2′‐arenesulfonyloxy‐5‐benzylidene‐thiazolidine‐2,4‐diones (TZDs) were synthesized and examined for their antiproliferative effects on a panel of carcinoma cell lines. Our results indicated that initial synthesis of 5‐[2′‐hydroxybenzylidene]‐2,4‐thiazolidinone (9) by Knoevenagel condensation followed by nucleophilic substitution with arylsulfonyl chlorides exhibited superior efficiency to the alternative synthetic route. Among tested compounds, only 8c and 8e showed significant antiproliferative activity against PC‐3 and BT474 cells with GI50 values of 8.4 and 20.6 μM, respectively. SKHep cells displayed interesting structure‐activity relationships in response to TZD derivatives treatment. Alkyl group‐substituted TZD analogs such as 8a (4‐Me, GI50, 9.4 μM) and 8k (4‐iso‐propyl, GI50, 9.8 μM) revealed better antiproliferative activity than those with bulkier alkyl groups. On the other hand, halogen‐substituted TZD analogs 8c, 8h, and 8i showed better antiproliferative activity against H460 cell line. Together, the new synthesized TZD derivatives 8a , 8b , 8c , 8d , 8e , 8f , 8g , 8h , 8i , 8j , 8k , 8l , 8m , 8n , 8o , 8p exhibited appreciable antiproliferative activity worth for further study. 相似文献
217.
Sherrod L. Maxwell Brian K. Culligan Angel Kelsey-Wall Patrick J. Shaw 《Journal of Radioanalytical and Nuclear Chemistry》2012,292(1):339-347
A new rapid method for the determination of actinides in food samples has been developed at the Savannah River Site Environmental
Lab (Aiken, SC, USA) that can be used for emergency response or routine food samples. If a radiological dispersive device
or improvised nuclear device event occurs, there will be a urgent need for rapid analyzes of many different environmental
matrices, as well as food samples, to support dose mitigation and protect general populations from radioactivity that may
enter the food chain. The recent accident at Fukushima nuclear power plant in March, 2011 reinforces the need to have rapid
analyzes for radionuclides in environmental and food samples. The new method to determine actinides in food samples utilizes
a furnace ashing step, a rapid sodium hydroxide fusion method, a lanthanum fluoride matrix removal step, and a column separation
process with stacked TEVA, TRU, and DGA resin cartridges. The furnace ashing and rapid fusion steps are performed in relatively
inexpensive, reusable zirconium crucibles. Alpha emitters are prepared using rare earth micro precipitation for counting by
alpha spectrometry. The method showed high chemical recoveries and effective removal of interferences. The determination of
actinides in food samples can be performed in less than 8 h for 10 g samples with excellent quality for emergency samples
using short count times. Larger food samples (100 g) may be processed in 24 h or less. The rapid fusion technique is a rugged
sample digestion method that ensures that any refractory actinide particles are effectively digested. This method can be used
to meet the derived intervention level guidelines recommended by the U.S. Food and Drug Administrations. 相似文献
218.
High-density silicon and silicon nitride cones 总被引:1,自引:0,他引:1
High-density cone-shaped silicon and silicon nitride have been synthesized on Si(1 0 0) substrates via plasma-assisted hot-filament chemical vapor deposition using a gas mixture of nitrogen, hydrogen and methane. Aligned silicon cones containing 3–10 at% C and N have been formed with less than 1 h growth. Further growth can lead to the increase of cone size and density, as well as to the formation of polycrystalline silicon nitride films on the tip and surface. The formation of these materials is thought to be due to the remodification of Si substrates under the effect of plasma and active C and N species. Different nucleation and growth styles were obtained under different growth conditions and reactive gas mixtures. 相似文献
219.
220.