全文获取类型
收费全文 | 94321篇 |
免费 | 10333篇 |
国内免费 | 1704篇 |
专业分类
化学 | 68438篇 |
晶体学 | 1333篇 |
力学 | 3732篇 |
综合类 | 8篇 |
数学 | 6669篇 |
物理学 | 26178篇 |
出版年
2022年 | 589篇 |
2021年 | 716篇 |
2020年 | 1745篇 |
2019年 | 3042篇 |
2018年 | 1651篇 |
2017年 | 1205篇 |
2016年 | 4292篇 |
2015年 | 4170篇 |
2014年 | 4461篇 |
2013年 | 6697篇 |
2012年 | 5285篇 |
2011年 | 5187篇 |
2010年 | 4991篇 |
2009年 | 4986篇 |
2008年 | 5085篇 |
2007年 | 4284篇 |
2006年 | 3860篇 |
2005年 | 3722篇 |
2004年 | 3361篇 |
2003年 | 3019篇 |
2002年 | 3585篇 |
2001年 | 4334篇 |
2000年 | 3407篇 |
1999年 | 1907篇 |
1998年 | 1122篇 |
1997年 | 1089篇 |
1996年 | 907篇 |
1995年 | 794篇 |
1994年 | 722篇 |
1993年 | 642篇 |
1992年 | 974篇 |
1991年 | 965篇 |
1990年 | 865篇 |
1989年 | 765篇 |
1988年 | 752篇 |
1987年 | 808篇 |
1986年 | 663篇 |
1985年 | 903篇 |
1984年 | 838篇 |
1983年 | 576篇 |
1982年 | 580篇 |
1981年 | 549篇 |
1980年 | 513篇 |
1979年 | 630篇 |
1978年 | 657篇 |
1977年 | 666篇 |
1976年 | 582篇 |
1975年 | 489篇 |
1974年 | 534篇 |
1973年 | 460篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
991.
Analysis of acyclovir by high performance capillary electrophoresis with on-column amperometric detection 总被引:1,自引:0,他引:1
The separation of acyclovir (ACV) by high performance capillary electrophoresis (HPCE) with on-column amperometric detection using alpha-amino-5-mercapto-3,4-dithiazole (AMD) as internal standard is described. The calibration line was linear in the range of 0.5-20 mg/L of ACV. The detection limit was 0.15 mg/L of ACV. Its recovery ranged from 98 to 101% with relative standard deviations (RSDs) from 1.9 to 3.2% (n = 5). This method was successfully used for determining ACV in some pharmaceuticals and human urine. Comparable results with HPCE with ultraviolet (UV) detection and amperometric detection were obtained. 相似文献
992.
993.
Alcohol dehydrogenase (ADH) has been immobilized on a nickel hexacyanoferrate modified microband gold electrode surface by a glutaraldehyde/bovine serum albumin (BSA) cross-linking procedure to provide a new amperometric sensor for the assay of ethanol. The resulting enzyme electrode exhibits excellent electrocatalysis for the oxidation of reduced nicotinamide-adenine dinucleotide (NADH). The amperometric determination is based on the electrochemical detection of NADH which is generated in the enzymatic reaction of ethanol with NAD(+) under catalysis of ADH. The influence of various experimental conditions was examined for the determination of the optimum analytical performance. The sensor responds rapidly to ethanol with a detection limit of (5.0 +/- 0.3) x 10(-7) mol 1(-1). The response current increases linearly with ethanol concentration up to 5 mmol 1(-1). The sensor remains relatively stable for about 1 week. 相似文献
994.
995.
T. Jabbar M. S. Subhani K. Khan A. Rashid S. D. Orfi A. Y. Khan 《Journal of Radioanalytical and Nuclear Chemistry》2003,258(1):143-149
A study on the concentration of natural and fallout radionuclides in environmental samples collected from different localities of Islamabad was performed. For the determination of gamma-emitters such as 238U, 232Th, 40K and 137Cs high purity germanium (HPGe) detector was used while for the analysis of 90Sr, a beta-emitter, liquid scintillation counting system was used. The indoor absorbed dose rate was measured by a CaF2 : Dy thermoluminescence detector. Other radiation parameters were also determined to evaluate the radiation hazard. All the results were well within the permissible limits showing that there is no radiation hazard in the environment of Islamabad. 相似文献
996.
M.Iqbal Choudhary SyedGhulam Musharraf Amtul Sami Atta‐ur‐Rahman 《Helvetica chimica acta》2004,87(10):2685-2694
The microbial transformation of (?)‐Ambrox® ( 1 ), a perfumery sesquiterpene, by a number of fungi, by means of standard two‐stage‐fermentation technique, afforded ambrox‐1α‐ol ( 2 ), ambrox‐1α,11α‐diol ( 3 ), ambrox‐1α,6α‐diol ( 4 ), ambrox‐1α,6α,11α‐triol ( 5 ), ambrox‐3‐one ( 6 ), ambrox‐3β‐ol ( 7 ), ambrox‐3β,6β‐diol ( 8 ), 13,14,15,16‐tetranorlabdane‐3,8,12‐triol ( 9 ), and sclareolide ( 10 ) (Schemes 1 and 2). Further incubation of compound 10 with Cunninghamella elegans afforded 3‐oxosclareolide ( 11 ), 3β‐hydroxysclareolide ( 12 ), 2α‐hydroxysclareolide ( 13 ), 2α,3β‐dihydroxysclareolide ( 14 ), 1α,3β‐dihydroxysclareolide ( 15 ), and 3β‐hydroxy‐8‐episclareolide ( 16 ) (Scheme 3). Metabolites 2 – 5, 12, 13 , and 16 were found to be new compounds. The major transformations include a reaction path involving hydroxylation, ether‐bond cleavage and inversion of configuration. Metabolites 11 – 16 of sclareolide showed significant phytotoxicity (Table 1). The structures of the metabolites were characterized on the basis of spectroscopic techniques. 相似文献
997.
The room temperature ionic liquid n‐butylpyridinium tetrafluoroborate (BPyBF4) is used as a ‘green’ recyclable alternative to classical molecular solvents for the cyclocondensation of α‐tosyloxyketones with 1‐aminoisoquinoline to prepare imidazo[2,1‐a]isoquinolines in good yields. 相似文献
998.
Facile synthesis of exfoliated and highly conductive poly(arylene disulfide)/graphite nanocomposites
Exfoliated graphite has been synthesized by first synthesizing H2SO4 intercalated compound in a H2O2‐H2SO4 mixture, followed by exfoliation under microwave irradiation. Poly(arylene disulfide)/graphite nanocomposites were then fabricated by absorbing cyclic(arylene disulfide) oligomers into the pores of exfoliated graphite. Subsequently, the nanocomposite precursor was subjected to heat treatment to carry out the in situ ring‐opening polymerization of the oligomers via free radical mechanism. The as‐prepared nanocomposite exhibited a exfoliated nanostructure as evidenced by transmission electron microscopy (TEM) observation. The nanocomposite with a very small amount of graphite, 5 wt%, possesses a highly electrical conductivity of 4 S/cm, therefore, many applications can be found as conductive materials. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
999.
Shuang‐Jun Lin Chang‐Heng Tan Shan‐Hao Jiang Yi‐Ming Li Da‐Yuan Zhu 《Helvetica chimica acta》2006,89(11):2789-2793
Four new iridoids, buergerinins B–E ( 1 – 4 ), along with three known iridoids, were isolated from the roots of Scrophularia buergeriana. Their structures were identified on the basis of spectroscopic analysis. 相似文献
1000.
New spirocyclic heterocycles 8, 16, 19/20, 25, 27 , and 30 derived from pyrimido[4,5‐b][1,4]diazepin]‐8′(9′H)‐one were synthesised by a tandem nitroso‐ene/Diels–Alder reaction of 4‐(alkenoylamino)‐5‐nitrosopyrimides. The crystal structure of 16 was established by X‐ray analysis. It is characterised by four pairs of intermolecular H‐bonds linking every two molecules in the unit cell. Sequential imine reduction and intramolecular condensation of the C(4′)‐(acylamino)‐pyrimido[4,5‐b][1,4]diazepines 27 and 30 led to the [1,4]diazepino[1,2,3‐gh]purines 28 / 29 and 31 , respectively. 相似文献