全文获取类型
收费全文 | 10759篇 |
免费 | 522篇 |
国内免费 | 72篇 |
专业分类
化学 | 7486篇 |
晶体学 | 118篇 |
力学 | 316篇 |
数学 | 936篇 |
物理学 | 2497篇 |
出版年
2023年 | 50篇 |
2022年 | 49篇 |
2021年 | 253篇 |
2020年 | 212篇 |
2019年 | 213篇 |
2018年 | 217篇 |
2017年 | 185篇 |
2016年 | 370篇 |
2015年 | 328篇 |
2014年 | 444篇 |
2013年 | 755篇 |
2012年 | 895篇 |
2011年 | 989篇 |
2010年 | 587篇 |
2009年 | 486篇 |
2008年 | 727篇 |
2007年 | 686篇 |
2006年 | 622篇 |
2005年 | 565篇 |
2004年 | 482篇 |
2003年 | 395篇 |
2002年 | 414篇 |
2001年 | 238篇 |
2000年 | 150篇 |
1999年 | 101篇 |
1998年 | 59篇 |
1997年 | 69篇 |
1996年 | 85篇 |
1995年 | 82篇 |
1994年 | 83篇 |
1993年 | 58篇 |
1992年 | 63篇 |
1991年 | 54篇 |
1990年 | 50篇 |
1989年 | 41篇 |
1988年 | 26篇 |
1987年 | 17篇 |
1986年 | 11篇 |
1985年 | 33篇 |
1984年 | 21篇 |
1983年 | 17篇 |
1982年 | 19篇 |
1981年 | 19篇 |
1980年 | 12篇 |
1979年 | 14篇 |
1978年 | 16篇 |
1977年 | 11篇 |
1976年 | 13篇 |
1975年 | 10篇 |
1972年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Numerical Algorithms - We develop a formal construction of a pointwise divergence-free basis in the nonconforming virtual element method of arbitrary order for the Stokes problem introduced in Zhao... 相似文献
2.
Ajay Gupta Fillip Kumar Sarkar Rajib Sarkar Ramen Jamatia Chang Yeon Lee Gajendra Gupta Amarta Kumar Pal 《应用有机金属化学》2020,34(9):e5782
Magnetically retrieval CuFe2O4@MIL-101(Cr) metal–organic framework was successfully prepared from easily available starting materials and characterized using various spectroscopic and analytical techniques such as powder X-ray diffraction, scanning electron microscopy, energy dispersive X-ray, transmission electron microscopy, elemental mapping, Fourier transform infrared spectroscopy, thermogravimetric analysis, X-ray photoelectron spectroscopy, Brunauer–Emmett–Teller, vibrating sample magnetometer, and inductively coupled plasma optical emission spectroscopy. The catalyst was then used in the synthesis of benzodiazepines containing a triazole moiety in water. The advantages of this protocol include high yields, reusability of the catalyst, and gram-scale synthesis. 相似文献
3.
Dr. Zhoulong Fan Katherine L. Bay Dr. Xiangyang Chen Zhe Zhuang Han Seul Park Dr. Kap-Sun Yeung Prof. Dr. K. N. Houk Prof. Dr. Jin-Quan Yu 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(12):4800-4807
A simple and efficient nitrile-directed meta-C−H olefination, acetoxylation, and iodination of biaryl compounds is reported. Compared to the previous approach of installing a complex U-shaped template to achieve a molecular U-turn and assemble the large-sized cyclophane transition state for the remote C−H activation, a synthetically useful phenyl nitrile functional group could also direct remote meta-C−H activation. This reaction provides a useful method for the modification of biaryl compounds because the nitrile group can be readily converted to amines, acids, amides, or other heterocycles. Notably, the remote meta-selectivity of biphenylnitriles could not be expected from previous results with a macrocyclophane nitrile template. DFT computational studies show that a ligand-containing Pd–Ag heterodimeric transition state (TS) favors the desired remote meta-selectivity. Control experiments demonstrate the directing effect of the nitrile group and exclude the possibility of non-directed meta-C−H activation. Substituted 2-pyridone ligands were found to be key in assisting the cleavage of the meta-C−H bond in the concerted metalation–deprotonation (CMD) process. 相似文献
4.
5.
Kyungmin Lim Do-Kyung Kim Jae Bum Jeong Suyoung Choi Swarup Biswas Alexandra Tibaldi 《Molecular Crystals and Liquid Crystals》2019,687(1):113-117
AbstractWe demonstrate the electrical properties of nano energy harvesters (NEHs) with various textiles for smart textiles that can be applied to the next generation wearable electronics. Output voltages and currents of NEHs with various fabrics, such as a cotton, rayon and wool that have different triboelectricity were measured. Cotton, rayon and wool shows the maximum output voltages of 1.250, 3.313 and 4.063 V, respectively. In addition, output currents of those textiles were 0.75, 4.4, 1.063 μA, respectively. Wool, in particular, which has the highest triboelectricity of 350 V exhibits the highest output voltage. 相似文献
6.
Santosh Kumar Sejy Lee Reju George Thomas Seung‐Jea Lee Hong‐Joon Lee In‐Kyu Park Yong Yeon Jeong Tae‐Ho Yoon Dong‐Chan Shin Jae‐Suk Lee 《Journal of polymer science. Part A, Polymer chemistry》2019,57(11):1165-1172
Self‐emulsion polymerization (SEP), a green route developed by us for the polymerization of amphiphilic monomers, does not require any emulsifier or an organic solvent except that the water‐soluble initiators such as 2,2′‐azobis[2‐(2‐imidazolin‐2‐yl)propane]dihydrochloride (VA‐044) and potassium persulfate (KPS) are only used. We report here the polymer nanoscaffolds from a number of amphiphilic monomers, which can be used for in situ encapsulation of a variety of nanoparticles. As a demonstration of the efficacy of these nanoscaffolds, the synthesis of a biocompatible hybrid nanoparticle (nanohybrid), prepared by encapsulating Fe3O4 magnetic nanoparticle (Fe3O4 MNPs) in poly(2‐hydroxyethyl methacrylate) in water, for MRI application is presented. The nanohybrid prepared following the SEP in the form of an emulsion does not involve the use of any stabilizing agent, crosslinker, polymeric emulsifier, or surfactant. This water‐soluble, spherical, and stable nanohybrid containing Fe3O4 MNPs of average size 10 ± 2 nm has a zeta potential value of ?41.89 mV under physiological conditions. Magnetic measurement confirmed that the nanohybrid shows typical magnetic behavior having a saturation magnetization (Ms) value of 32.3 emu/g and a transverse relaxivity (r2) value of 29.97 mM?1 s?1, which signifies that it can be used as a T2 contrast agent in MRI. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 相似文献
7.
Afif Ahmed Radenahmad Nikdalila Rahman Seikh Mohammad Habibur Torino Nico Saqib Muhammad Hossain Shahzad Park Jun-Young Azad Abul Kalam 《Journal of Solid State Electrochemistry》2022,26(1):111-120
Journal of Solid State Electrochemistry - Protonic ceramic fuel cells have become extremely interesting due to their high power output at the intermediate temperature range... 相似文献
8.
Yongho Shin Tae Yeon Kong Jae Cheol Cheong Jin Young Kim Jae Il Lee Hye Suk Lee 《Biomedical chromatography : BMC》2019,33(9)
A liquid chromatography–tandem mass spectrometric method for the simultaneous determination of 75 abuse drugs and metabolites, including 19 benzodiazepines, 19 amphetamines, two opiates, eight opioids, cocaine, lysergic acid diethylamide, zolpidem, three piperazines and 21 metabolites in human hair samples, was developed and validated. Ten‐milligram hair samples were decontaminated, pulverized using a ball mill, extracted with 1 mL of methanol spiked with 28 deuterated internal standards in an ultrasonic bath for 60 min at 50°C, and purified with Q‐sep dispersive solid‐phase extraction tubes. The purified extracts were evaporated to dryness and the residue was dissolved in 0.1 mL of 10% methanol. The 75 analytes were analyzed on an Acquity HSS T3 column using gradient elution of methanol and 0.1% formic acid and quantified in multiple reaction monitoring mode with positive electrospray ionization. Calibration curves were linear (r ≥ 0.9951) from the lower limit of quantitation (2–200 pg/mg depending on the drug) to 2000 pg/mg. The coefficients of variation and accuracy for intra‐ and inter‐assay analysis at three QC levels were 4.3–12.9% and 89.2–109.1%, respectively. The overall mean recovery ranged from 87.1 to 105.3%. This method was successfully applied to the analysis of 11 forensic hair samples obtained from drug abusers. 相似文献
9.
Park Kyueun Kim Youngjin Lee Kyung Jin 《Journal of Radioanalytical and Nuclear Chemistry》2019,319(2):487-531
Journal of Radioanalytical and Nuclear Chemistry - An extensive series of evaluations have been performed as part of an IAEA coordinated research project to study a set of nuclear reactions that... 相似文献
10.
AbstractIn this study, as a continuous effort for searching efficient blue-emitting materials, we designed and synthesized materials based on indeno[1,2-a]arene. OLED devices using these materials were fabricated in the following sequence; ITO (180?nm)/N,N'-diphenyl-N,N'-(2-napthyl)-(1,1'-phenyl)-4,4'-diamine (NPB) (50?nm)/emitting materials (30?nm)/4,7-diphenyl-1,10-phenanthroline (Bphen) (30?nm)/Liq/Al (2/100?nm). Particularly, a device using 7,7-dimethyl-7H-indeno[1,2-a]pyrene as emitter showed maximum values of luminous efficiency, power efficiency, and external quantum efficiency of 1.10?cd/A, 0.49?lm/W, 1.47% at 20?mA/cm2, respectively with CIE (x,y) coordinates of (0.15, 0.08) at 6.0V. 相似文献