全文获取类型
收费全文 | 138482篇 |
免费 | 22863篇 |
国内免费 | 11729篇 |
专业分类
化学 | 108041篇 |
晶体学 | 1348篇 |
力学 | 6856篇 |
综合类 | 585篇 |
数学 | 14538篇 |
物理学 | 41706篇 |
出版年
2024年 | 344篇 |
2023年 | 2055篇 |
2022年 | 3554篇 |
2021年 | 3904篇 |
2020年 | 4957篇 |
2019年 | 5868篇 |
2018年 | 4209篇 |
2017年 | 3724篇 |
2016年 | 7543篇 |
2015年 | 7630篇 |
2014年 | 8464篇 |
2013年 | 10861篇 |
2012年 | 11730篇 |
2011年 | 11330篇 |
2010年 | 8788篇 |
2009年 | 8592篇 |
2008年 | 8767篇 |
2007年 | 7598篇 |
2006年 | 6797篇 |
2005年 | 6101篇 |
2004年 | 4963篇 |
2003年 | 4144篇 |
2002年 | 4630篇 |
2001年 | 3575篇 |
2000年 | 3248篇 |
1999年 | 2535篇 |
1998年 | 1930篇 |
1997年 | 1827篇 |
1996年 | 1874篇 |
1995年 | 1530篇 |
1994年 | 1393篇 |
1993年 | 1204篇 |
1992年 | 1092篇 |
1991年 | 924篇 |
1990年 | 811篇 |
1989年 | 637篇 |
1988年 | 573篇 |
1987年 | 449篇 |
1986年 | 441篇 |
1985年 | 441篇 |
1984年 | 296篇 |
1983年 | 232篇 |
1982年 | 197篇 |
1981年 | 163篇 |
1980年 | 158篇 |
1979年 | 123篇 |
1977年 | 108篇 |
1976年 | 103篇 |
1974年 | 104篇 |
1973年 | 114篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Summary A theoretical treatment is presented which considers differences between the composition of the mobile phase and solvents
that are incorporated into the bonded phase via preferential sorption. Equations are derived and used to analyze retention
data for various homologs chromatographed under reversed-phase conditions using alkyl bonded phases and combinations of water-methanol,
water-acetonitrile and watertetrahydrofuran as mobile phases. In the case of water-methanol the surface phase and bulk mobile
phase compositions are similar. However, significant differences in composition between the two phases are observed when binary
combinations of water-acetonitrile and water-tetrahydrofuran are used as the cluents. 相似文献
992.
Timothy B. Hutson Ming J. W. Chang Joseph T. Keller David J. Long 《Mikrochimica acta》1988,94(1-6):339-341
Fourier transform infrared techniques were used to monitor mammalian cell growth plated on attenuated total reflection (ATR) crystals. Consistently, the growth kinetics plots generated from the obtained spectra demonstrated a sigmoidal curve representing a sequence of slow, rapid, then tapering cell growth which correlated well with non-spectral cell growth determinations. Significant advantages over traditional methods of measuring cell growth kinetics are demonstrated. The technique has promising potential to be used to study events in areas such as toxicology and cell biology. 相似文献
993.
用火焰原子吸收法测定了2000例甲亢病人的血清镁含量及1200例天津市正常人群血清镁含量,结果显示,甲亢病人血清镁含量显著低于正常人群,有显著统计意义(P〈0.01)。提示:甲亢病人血清镁含量对甲亢病诊断及治疗过程的镁的摄入补充有重要的意义。 相似文献
994.
A procedure for the simultaneous time-resolved fluoroimmunoassay for phenobarbital and phenytoin, based on the use of europium- and samarium-labeled haptens, has been investigated. These lanthanide ions are bound to the haptens by means of the anhydride of diethylenetriaminepentaacetic acid. The antibody is immobilized onto immunoplate in which samples are assayed in competitive immunoassay. After the immunoreactions and dissociation with a fluorescence enhancement solution, the fluorescence intensity is measured. The detection limits of the assay are, respectively, 20 ng/ml for phenobarbital and 50 ng/ml for phenytoin. Results obtained with the proposed methods correlate well (CV <10%). The inter-reactions between phenobarbital, phenytoin, and their antibodies are studied. 相似文献
995.
叙述了同步辐射白光全反射X射线荧光分析的实验装置,给出了几种标准物质TXRF实验的检出限,并对实验结果进行了讨论。 相似文献
996.
This research applies semiconductor photocatalysts, which are formed by metal ion exchange on the surface of kaolinite catalyst with cations, to the study of photocatalytic degradation of 4‐chlorophenol. The analysis results of catalyst properties shows that, after sintering at 400 °C, kaolinite catalyst has a particle size of between 10–100 nm indicating the nano level of synthesized catalysts. Under the same condition, kaolinite‐Ag/Zn catalyst works better in degradation efficiency than single kaolinite‐Ag and kaolinite‐Zn catalysts. Kaolinite‐Zn catalyst declines in degradation efficacy after 150 minutes and performs poorer than the other three types of kaolinite catalysts. In the experiments of different amounts of catalysts, when the concentration exceeds 0.1 wt%, utilization of light energy and degradation efficiency will be reduced due to shielding effect. When at different pH values, the higher the pH value, the more OH‐will be released and that is beneficial for reaction with substances and the increase of reaction rate. Finally multivariate analysis proves that there is one determining factor that influences the photocatalytic degradation of 4‐chlorophenol in kaolinite catalysts, named as “the factor with intermediates competition degree,” the one affecting the 4‐CP degradation at different weight percentages that is referred to as the “shielding effect factor.” 相似文献
997.
Ping ZHENG Wei Lin SUN Zhi Quan SHEN 《中国化学快报》2005,16(10):1413-1416
N-2-Thiazolylacrylamide (NTA) was polymerized by a radical route to obtain the polymer in good yield. The polymer with a pendent heterocyclic group is soluble in common organic solvents, which allow to prepare the corresponding metal complexes with higher loads easily. FTIR, ^1H NMR, elemental analysis, and energy-dispersive X-Ray spectroscopy (EDX) were applied to characterize these materials. The magnetic behavior of Fe(Ⅱ) and Nd(Ⅲ) complexes of poly(N-2-thiazolylacrylamide) was examined by a PPMS-9T magnetometer, exhibiting the characteristics of a soft ferromagnet. It is found that the Nd(Ⅲ) complex has an extremely high relative saturation magnetization of 35 emu/g. 相似文献
998.
[reaction: see text] A new method for the synthesis of alpha(2 --> 9) oligosialic acids is developed using phosphite sialyl donors that are protected with a C-5 N-trifluoroacetyl (NHTFA) substituent. Compared with conventional donors, these donors gave a higher degree of alpha-anomeric selectivity during glycosidic bond formation and better yields during iterative sialylation in the synthesis of oligosialic acids. 相似文献
999.
Griffiths WJ Alvelius G Liu S Sjövall J 《European journal of mass spectrometry (Chichester, England)》2004,10(1):63-88
Neutral oxosteroids have been derivatised with Girard T and P hydrazine reagents to give the corresponding Girard hydrazone quaternary ammonium salts. Both Girard T (GT) and Girard P (GP) hydrazones of oxosteroids give very intense [M](+) ion signals in electrospray (ES) mass spectra and fragment within the ES interface and collision cell to give characteristic fragment ions. GT and GP derivatives give informative high-energy collision-induced dissociation spectra, from which the structure of the precursor oxosteroid can be determined. Both charge-remote and charge-mediated mechanisms are responsible for the formation of the fragment ions at high collision-energy. 相似文献
1000.