全文获取类型
收费全文 | 105635篇 |
免费 | 18108篇 |
国内免费 | 10126篇 |
专业分类
化学 | 71435篇 |
晶体学 | 1220篇 |
力学 | 6947篇 |
综合类 | 540篇 |
数学 | 11933篇 |
物理学 | 41794篇 |
出版年
2024年 | 369篇 |
2023年 | 2137篇 |
2022年 | 3651篇 |
2021年 | 3867篇 |
2020年 | 4262篇 |
2019年 | 4144篇 |
2018年 | 3559篇 |
2017年 | 3294篇 |
2016年 | 5200篇 |
2015年 | 4956篇 |
2014年 | 6045篇 |
2013年 | 7803篇 |
2012年 | 9451篇 |
2011年 | 9779篇 |
2010年 | 6456篇 |
2009年 | 6175篇 |
2008年 | 6549篇 |
2007年 | 6015篇 |
2006年 | 5489篇 |
2005年 | 4600篇 |
2004年 | 3408篇 |
2003年 | 2674篇 |
2002年 | 2418篇 |
2001年 | 1988篇 |
2000年 | 1767篇 |
1999年 | 2082篇 |
1998年 | 1850篇 |
1997年 | 1728篇 |
1996年 | 1893篇 |
1995年 | 1512篇 |
1994年 | 1464篇 |
1993年 | 1168篇 |
1992年 | 1071篇 |
1991年 | 986篇 |
1990年 | 797篇 |
1989年 | 566篇 |
1988年 | 467篇 |
1987年 | 383篇 |
1986年 | 374篇 |
1985年 | 318篇 |
1984年 | 242篇 |
1983年 | 154篇 |
1982年 | 142篇 |
1981年 | 106篇 |
1980年 | 76篇 |
1979年 | 44篇 |
1978年 | 34篇 |
1976年 | 36篇 |
1975年 | 33篇 |
1974年 | 45篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
941.
Cheng-shen Zhu Xin Kang Su-qin He Liu-yang Wang Li-yun Lu College of Materials Engineering Zhengzhou University Zhengzhou China 《高分子科学》2002,(6):551-557
The montmorillonites (MMTs), layered, smectite-type silicates, were premodified by two different methods priorto the polymer melt intercalation. In one case MMTs were modified with cetyltrimethylammonium bromide (CTAB), andtermed as organomontmorillonites (OMMTs); in the other case MMTs were modified by nylon, and the products were calledmodified montmorillonites (MMMTs). The effects of CTAB and nylon on the MMTs were investigated by using TG andWAXD. The results show that interlayer spacings of CTAN and nylon modified MMTs are larger than that of sodium MMTs.Then, polyamide 66 (PA 66)/MMT nanocomposites were obtained through the method of melt intercalation of polymers. Thenanocomposites were characterized by WAXD, TEM and Molau experiments. The results indicate that the MMTs dispersehomogeneously in the PA 66 matrix. The mechanical properties of nanocomposites, such as tensile properties and flexuralproperties, were also measured and show a tendency to increase with increase of MMT content and reach the maximumvalues at 5phr MMT content. The heat distortion temperature (HDT) of the nanocomposites (7 phr) is about 32 K higher thanthat of pure PA 66. 相似文献
942.
煤浸出液中的阴阳离子测定及其与水煤浆成浆性的关系 总被引:4,自引:4,他引:4
用离子色谱法对十种煤(其灰分为3.03—8.20%)浸出液中的阴阳离子进行了测定,考察了它们与煤的成浆性的关系。计算机分析表明,矿物对煤成浆性的影响有两方面:一方面是可溶性矿物对成浆性的不利影响,另一方面是矿物密度对堆积效率的有利贡献。实验表明,硫酸根离子对煤成浆性的影响尤为突出,它综合反映了高价金属离子的总影响。 相似文献
943.
944.
Three new polyoxygenated briarane-type diterpenoids, briaexcavatolides X-Z (1-3), have been isolated from the gorgonian coral Briareum excavatum. The structures, including the relative configurations of briaranes 1-3, were elucidated by spectroscopic methods, particularly in 1D and 2D NMR experiments. The configuration of briarane 1 was further supported by molecular mechanics calculations. 相似文献
945.
946.
Shu-Lin Ma Zong-Hui Jiang Dai-Zheng Liao Shi-Ping Yan Geng-Lin Wang 《Transition Metal Chemistry》1994,19(5):531-533
Summary Two novel trinuclear complexes were prepared, namely [Cu2(oxae)2(H2O)2M] (ClO4)2, [oxae = N,N-bis(2-aminoethyl) oxamido dianion; M = Co and Ni]. Based on elemental analyses, conductivity measurements and i.r. spectra, the complexes are proposed to have extended oxamidobridged structures. The magnetic susceptibility of [Cu2-(oxae) 2(H2O)2Co](ClO4)2 were measured over the 4–300 K range and the observed data were successfully simulated by an equation based on the spin Hamiltonian, =–2J(1·2·2·3). The exchange integral, J, was found to be equal to –29.2 cm–1, indicating an antiferromagnetic spin-exchange interaction between the adjacent metal ions. 相似文献
947.
XIE Mao-Song YANG Xu CHEN Wen-Heng TAO Long-Xiang WANG Xuc-Lin XU Gui-Fen 《天然气化学杂志》1996,5(3):210-221
IntroductionMethancisthcmaJorcomponcntofnaturalgasanditscatalyticconvcrsiontodcsiredchemicalproductsorliquidfiJcIisnotonl}'apromisingapproachtotheutilizationofnaturalgasrcsourccbutalsoagrcatsubjcctforcatalysissciencctt'hichdcaIst"iththcactivationofsmallmolcculesThcx"orldrcscrvcofnaturalgashasbccnexplorcdasaboutl382562xl()8m3IllTheMTGprocessdcvclopedbythcMobilcorpcangctliquidfuelfrommethancthroughsteamreformingofmethanctoproduccsynthcsisgaswhichisassociatedt'ithamaJorityofthecostsofthcprocc… 相似文献
948.
949.
In this study, a rapid and sensitive high performance liquid chromatography-inductively coupled plasma-mass spectrometry (HPLC-ICP-MS) determination of primary As species in fish tissues and urine is reported. The separation was achieved on an Altima C18 column with a mobile phase containing citric acid and hexanesulfonic acid (pH 4.5). As(V), monomethylarsonic acid (MMA), As(III), dimethylarsinic acid (DMA) and arsenobetaine (AsB) were separated in less than 4 min with retention times of 83, 99, 130, 166 and 208 s, respectively. This separation of five species in less than 4 min should be attractive to those interested in As speciation. The quantification limits were 44, 56, 94, 64, 66 ng l(-1) and the relative standard deviations (R.S.D.) for day-to-day injections of As at 2 mug l(-1) were 2.0, 3.1, 2.4, 3.8 and 4.0%. The procedure was tested using two reference materials (DORM-2 dogfish muscle tissue, NIST SRM 2670 Freeze-dried Urine, normal level) and then applied to real-world samples. The results obtained demonstrate the suitability of the procedure for screening and quantification at physiological levels of primary As species in biological samples. 相似文献
950.
用统计模拟分光光度法测定复方消咳新片4个组分含量。按均匀设计表制备合成样品,绘制溶液的UV-VIS吸收曲线,获得有限但足够的实验数据,用逐步回归法构造反映该复方制剂组分在灵敏波长的吸光度-组分含量经验关系的“最优”数学模型,用改进单纯形法寻优,求出未知样品的各组分含量。磺胺甲基异恶唑、甲氧苄胺嘧啶、盐酸溴已新、枸橼酸维静宁的回收率分别为1003%、1004%、999%、990%,标准差分别为091%、14%、12%、39%。 相似文献