全文获取类型
收费全文 | 7991篇 |
免费 | 1257篇 |
国内免费 | 751篇 |
专业分类
化学 | 5619篇 |
晶体学 | 132篇 |
力学 | 475篇 |
综合类 | 76篇 |
数学 | 787篇 |
物理学 | 2910篇 |
出版年
2024年 | 20篇 |
2023年 | 173篇 |
2022年 | 254篇 |
2021年 | 273篇 |
2020年 | 369篇 |
2019年 | 342篇 |
2018年 | 289篇 |
2017年 | 244篇 |
2016年 | 404篇 |
2015年 | 387篇 |
2014年 | 517篇 |
2013年 | 594篇 |
2012年 | 659篇 |
2011年 | 694篇 |
2010年 | 459篇 |
2009年 | 374篇 |
2008年 | 500篇 |
2007年 | 426篇 |
2006年 | 380篇 |
2005年 | 321篇 |
2004年 | 215篇 |
2003年 | 219篇 |
2002年 | 166篇 |
2001年 | 124篇 |
2000年 | 154篇 |
1999年 | 152篇 |
1998年 | 131篇 |
1997年 | 131篇 |
1996年 | 153篇 |
1995年 | 111篇 |
1994年 | 110篇 |
1993年 | 90篇 |
1992年 | 78篇 |
1991年 | 71篇 |
1990年 | 74篇 |
1989年 | 48篇 |
1988年 | 50篇 |
1987年 | 37篇 |
1986年 | 37篇 |
1985年 | 26篇 |
1984年 | 22篇 |
1983年 | 15篇 |
1982年 | 19篇 |
1981年 | 15篇 |
1980年 | 11篇 |
1979年 | 8篇 |
1975年 | 5篇 |
1974年 | 5篇 |
1970年 | 12篇 |
1937年 | 5篇 |
排序方式: 共有9999条查询结果,搜索用时 15 毫秒
951.
Ni Hou Yu Chen Shiyong Yu Zongliang Quan Chenhua Pan Yulin Deng Lina Geng 《Chromatographia》2014,77(19-20):1339-1346
The use of microfluidic chip-based two-dimensional separation holds great promise in the proteomics field, given its portability, simplicity, speed, efficiency, and throughput. However, inclusion of sodium dodecyl sulfate, reported to be necessary for increasing protein-resolving capability, was also accompanied by the loss of both protein conformation and biological function. Here, we describe separation of native proteins by introducing blue native gel electrophoresis into isoelectric focusing and gel electrophoresis (IEF/CGE)-coupled protein two-dimensional microfluidic chip electrophoresis. After assessing the influence of various experimental conditions, the best separation ability and reproducibility of blue native IEF/CGE (IEF/BN-CGE) chip electrophoresis achieved until now were demonstrated no matter whether with a simple simulated mixture or with a complex mixture of total Escherichia coli proteins. Finally, instead of theoretical calculations, the image analysis technique was also used for the first time to quantitatively evaluate the actual peak capacities of chip electrophoresis. According to the number of features abstracted in the electrophoresis patterns, the superiority of the IEF/BN-CGE two-dimensional microfluidic chip electrophoresis was then exhibited quantitatively. The high native protein separation performance makes this established chip electrophoresis method possible for further application in widely needed drug screening, analysis of bio-molecular function, and assays of protein–protein interactions. 相似文献
952.
Yu-Ping?Xu Min?YangEmail author Dong-Hui?Pan Li-Zhen?Wang 《Journal of Radioanalytical and Nuclear Chemistry》2011,288(1):157-161
The aim of this study was to examine the radioiodinating condition of betulinic acid and understand the possibility of 131I–betulinic acid (131I–BA) as a potential tumor radiotherapy agent through in vitro uptake and in vivo biodistribution studies 131I–BA was prepared by the reaction of betulinic acid with Na131I in the presence of hydrogen peroxide, and then purified by HPLC. The labeling yield was about 80%, and the radiochemical
purity was greater than 95%. 131I–BA was found to be stable at 4 °C in saline containing 1% ethanol. In vitro studies showed that 131I–betulinic acid accumulated in the cancer cell lines (BEL-7402 and NCI-H446) in comparison with free 131I−. In vivo biodistribution study in KM mice bearing HepA tumor showed that 131I–BA stayed longer time in tumors than free 131I−. A significant differences were seen in tumor/muscle ratio at 4 h postinjection between 131I–BA and free 131I−. In vivo and in vitro studies showed the higher fraction of 131I–BA can be utilized for therapy and a higher dose will be delivered per targeting event. 131I–BA is a promising radiopharmaceutical in nuclear medicine, especially for hepatocellular tumor targeted radionuclide brachytherapy. 相似文献
953.
954.
Nucleophilic thiol-acrylate Michael reaction between a hydrophobic thiol and hydrophilic acrylate derivative generated a nonionic surfactant with acid-labile β-thiopropionate linker. Micellization of the surfactant, its ability to encapsulate hydrophobic dye, acid-induced disruption of the aggregate and pH-selective dye release profile have been revealed in this report. The micellar aggregates were found to be stable under neutral conditions, but they could be disrupted in acidic pH (5.3), and thus the encapsulated hydrophobic dye molecules could be selectively released. Appropriate control experiments revealed that the sulfur atom in the β-position is essential for acidic hydrolysis of the ester functionality of the surfactant. 相似文献
955.
Zhao XD Fan HM Liu XY Pan H Xu HY 《Langmuir : the ACS journal of surfaces and colloids》2011,27(7):3224-3228
Tuning the adhesive force on a superhydrophobic MnO(2) nanostructured film was achieved by fabricating different patterns including meshlike, ball cactus-like, and tilted nanorod structures. The marvelous modulation range of the adhesive forces from 130 to nearly 0 μN endows these superhydrophobic surfaces with extraordinarily different dynamic properties of water droplets. This pattern-dependent adhesive property is attributed to the kinetic barrier difference resulting from the different continuity of the three-interface contact line. This finding will provide the general strategies for the adhesion adjustment on superhydrophobic surfaces. 相似文献
956.
ZnS hollow microspheres were synthesized by a dl ‐aspartic acid mediated hydrothermal route. dl ‐aspartic acid plays an important role as crystal growth soft template, which regulates the release of Zn2+ ions for the formation of ZnS hollow spheres. The formation of these hollow spheres was mainly attributed to an Ostwald ripening process. The products were characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), electron diffraction (ED), UV/Vis spectroscopy (UV), and photoluminescence (PL). The shells of the microspheres were composed of ZnS quantum dots (QDs) with the average size of 2.31 nm. The average microspheres diameter is 0.5–3.5 μm. The shell thickness of the hollow sphere is ≈?300 nm. The optical bandgap energy increased significantly compared to the bulk ZnS material due to the strong quantum confinement effect. Two strong emissions at ≈?425 nm and ≈?472 nm in the photoluminescence (PL) spectrum of ZnS hollow microspheres indicate strong quantum confinement because of the presence of QDs. 相似文献
957.
This work describes a novel droplet-based microfluidic device, which enables sequential droplet processing for rapid DNA extraction. The microdevice consists of a droplet generation unit, two reagent addition units and three droplet splitting units. The loading/washing/elution steps required for DNA extraction were carried out by sequential microfluidic droplet processing. The movement of superparamagnetic beads, which were used as extraction supports, was controlled with magnetic field. The microdevice could generate about 100 droplets per min, and it took about 1 min for each droplet to perform the whole extraction process. The extraction efficiency was measured to be 46% for λ-DNA, and the extracted DNA could be used in subsequent genetic analysis such as PCR, demonstrating the potential of the device for fast DNA extraction. 相似文献
958.
Alexei A. Belik Pan?e Naumov Jungeun Kim Shunsuke Tsuda 《Journal of solid state chemistry》2011,184(11):3128-3133
Low-temperature structural properties of the synthetic mineral libethenite Cu2PO4OH were investigated by single-crystal X-ray diffraction, synchrotron X-ray powder diffraction, specific heat measurements, and Raman spectroscopy. A second-order structural phase transition from the Pnnm symmetry (a=8.0553(8) Å, b=8.3750(9) Å, c=5.8818(6) Å at 180 K) to the P21/n symmetry (a=8.0545(8) Å, b=8.3622(9) Å, c=5.8755(6) Å, β=90.0012(15) at 120 K) was found at 160 K during cooling. At 120 K, the monoclinic angle is 90.0012(15) from single crystal X-ray data vs 90.083(1) from powder X-ray diffraction data. The P21/n–to–Pnnm transition may be a general feature of the adamite-type compounds, M2XO4OH. 相似文献
959.
Wenwu Zhao Shilie Pan Jian Han Jiyong Yao Yun Yang Junjie Li Min Zhang Lian Han Zhang Yin Hang 《Journal of solid state chemistry》2011,184(11):2849-2853
A new compound, Pb2BO3F, has been grown by high temperature solution method from the PbO–PbF2–B2O3 system for the first time. The crystal structure of this compound has been identified by single crystal X-ray diffraction analysis. It crystallizes in the hexagonal system, space group P63/m (No. 176) with unit-cell parameters a=7.2460(3) Å, c=14.5521(17) Å, Z=6, V=661.69(9) Å3. Its structure was solved by the direct methods and refined to R1=0.0163 and wR2=0.0367. The structure of Pb2BO3F consists of the distorted PbO3F2 groups and BO3 triangles, which are all symmetric with each other in the gestalt structure to the extent that the Pb2BO3F compound crystallizes in the symmetric space group. The powder X-ray diffraction pattern of the Pb2BO3F has been measured. The BO3 functional groups presented in the sample were identified by FTIR spectrum. The DTA curve of Pb2BO3F suggests that Pb2BO3F melts congruently at 448 °C. 相似文献
960.
Xinchun Li Jianbin Pan Fan Yang Jun Feng Jinyuan Mo Zuanguang Chen 《Mikrochimica acta》2011,174(1-2):123-130
We report on a simple amperometric detector for use in microchip capillary electrophoresis. A disposable syringe serves as the electrode holder that is fixed at the outlet of the separation channel. A carbon paste electrode is used to detect dopamine (DA) and catechol (CA) after electrophoretic separation. The two model analytes were well separated within 60 s. The response is linear in the concentration range from 4 to 500???M, and the detection limit is 1.2???M for DA (S/N = 3:1). The relative standard deviations of the inter-run and inter-electrode peak currents, respectively, are 2.8% and 5.7% for DA, and 3.9% and 6.5% for CA. Favorable column efficiency (expressed by the theoretical plate number which is 5.3 × 104 m-1 for DA) is achieved. The method was successfully applied to the separation and detection of 3-aminophenol (3-AP) in an injection powder containing sodium 4-aminosalicylate. The detection limit of 3-AP is as low as 1.7???M, which meets the demand of the impurity test. The facile assembly allows convenient replacement of working electrodes and improves the longevity of the microanalytical system. Figure
Voltammetric behaviors of 3-AP and 4-AS at carbon paste electrode (CPE), and microchip electrophoresis-amperometry with CPE for the two analytes. 相似文献