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81.
High-performance thin-layer chromatography has been used for separation and quantification of nitroguanidine and guanidine
nitrate, for online and off-line quality control of synthesis. The compounds were separated on silica gel 60 F254 layers with dioxane–tetrahydrofuran 1:1 (v/v), as mobile phase. UV detection was performed at 210 and 265 nm for guanidine nitrate and nitroguanidine, respectively. Quantitative
analysis was performed by absorbance densitometry and use of peak area. Validation was performed taking into consideration
the special features of the method. 相似文献
82.
The molecular structure of samarium dibromide has been studied by electron diffraction at T
exp = 1250(50) K. The molecule has C2v symmetry; the internuclear distance Rg(Sm–Br) = 274.5(5) pm; g =131(6)°. The vibration frequencies were estimated from the experimental values of the mean square vibration amplitudes. 相似文献
83.
锌—镉法测定天然水中硝酸盐的盐误差及其解决方法 总被引:9,自引:0,他引:9
研究了锌-镉法测定天然水中硝酸盐的盐误差,发现水中含盐量对还原率有重大影响,但在盐度为1%以后还原率基本不变;加入人工海盐(1.5g/50ml水样)可消除盐误差.由此建立了没有盐误差的新的锌-镉法.方法相对标准偏差小于3%,回收率为98%~102%,与镉-铜法对比,两种方法的相对偏差小于8%. 相似文献
84.
The formal synthesis of antimicrobial diterpene udoteatrial hydrate (1) is described in nine steps. Diol 6 used as starting material. The key intermediate 4 was obtained from bicyclic ketone 5 via the key Norrish type I reaction. 相似文献
85.
Qing LI Hui LI Bin SU Xiang Bao MENG Meng Shen CAI Zhong Jun LI* Department of Chemical Biology School of Pharmaceutical Sciences National Research Laboratory of Natural Biomimetic Drugs Peking University Beijing 《中国化学快报》2002,13(4):303-305
Our previous paper1,2reported the results of selective synthesis of mannose type glycosides and their dimers in our attempt to synthesize derivatives of N-acetyllacto- samine, which could have potential activity of anti-metastasis3. Further studies on the glycosylation of the accepters exploiting glycosyl nitrate instead of the acetate as donor showed interesting chemoselectivity between the two kinds of donor, namely, the glucose type and the mannose type. The reactivity difference of the t… 相似文献
86.
Christine Bonal Jean-Pierre Morel Nicole Morel-Desrosiers 《Journal of solution chemistry》1998,27(4):361-372
The apparent equilibrium constants and enthalpies of complexation of Nd3+, Sm3+, Eu3+, and Gd3+ by xylitol in aqueous solutions containing NaNO3 at an ionic strength of 2.0 mol-kg–1 have been determined by microcalorimetry at 25°C. Since nitrate anion weakly complexes the lanthanide cations, these values are analyzed in terms of competition between xylitol and NO
3
-
The method leads to the apparent equilibrium constants and enthalpies of complexation of the lanthanide cations by NO
3
-
at this particular ionic strength. Despite the difficulties encountered in characterizing rather weak associations, the results are, whenever comparison is possible, in good agreement with those obtained by direct microcalorimetry. The advantage of this competition method is that it can be used when the enthalpic effects are too weak and insufficiently concentration dependent for direct microcalorimetric determination. In the present case, it allows us to thermodynamically characterize the formation of SmNO
3
2+
and EuNO
3
2+
, processes we have not been able to study directly. 相似文献
87.
Tarek A.?SalamaEmail author Bernd?Lackner Heinz?Falk 《Monatshefte für Chemie / Chemical Monthly》2003,134(8):1113-1119
Summary. An efficient synthesis of tri-O-methylemodin aldehyde was achieved via bromination of tri-O-methylemodin utilizing N-bromosuccinimide yielding the monobromo and dibromo derivatives. Sommelet reaction of the monobromomethyl derivative as well as hydrolysis of the dibromomethyl analog with aqueous silver nitrate afforded the protected aldehyde in good yield. Accordingly, both bromo derivatives can be used even when they are obtained as a mixture of the bromination reaction, which could not be controlled easily to yield the bromo products selectively. From the aldehyde the tri-O-methylemodin nitrile was prepared in a one-pot reaction using hydroxylamine-O-sulfonic acid.Received February 18, 2003; accepted March 3, 2003
Published online June 2, 2003 相似文献
88.
Gas hydrates are non-stoichiometric crystalline compounds of water with gas at a certain temperature and pressure. Compared to the thermodynamics of hydrate formation, our knowledge on the kinetics aspect is rather immature. It is well known that the kinetics of hydrate formation/dissociation plays an important role in many industrial cases, such as the exploitation of methane hydrate underground, the storage and transportation of natural gas in solid hydrate state, the inhibition of hydrate i… 相似文献
89.
The aqueous synthesis and electrochemical properties of nanocrystalline MxV2O5Ay·nH2O are described. It is easily and quickly prepared by precipitation from acidified vanadate solutions. MxV2O5Ay·nH2O has been characterized by X-ray powder diffraction, electron microscopy, TGA, chemical analyses, and electrochemical studies. The atomic structure is related to that of xerogel-derived V2O5·nH2O. In MxV2O5Ay·nH2O, M is a cation from the starting vanadate salt and A is an anion from the mineral acid. This material exhibits high, reversible Li capacity and may be considered for use in a cathode in primary and secondary batteries. The lithium capacity of an electrode composed of MxV2O5Ay·nH2O/EPDM/carbon (88/4/8) is ∼380(mA h)/g (C/80 rate) and the energy density is ∼1000(W h)/kg (120-μm-thick cathode, 4-1.5 V, versus Li metal anode). Critical parameters identified in the synthesis of MxV2O5Ay·nH2O, with respect to achieving high Li-ion insertion capacity, are acid/vanadium ratio, starting vanadate salt, and temperature. Inclusion of carbon black in the synthesis yields a composite that maintains the high Li capacity, lowers the electrochemical-cell polarization, and preserves the lithium capacity at higher discharge rates. Li-ion coin cells, using pre-lithiated graphite anodes, exhibit electrochemical performance comparable to that of Li-metal coin cells. 相似文献
90.
V. Anuradha 《Tetrahedron letters》2006,47(28):4933-4935
Highly regiospecific mononitration of phenols and substituted phenols is accomplished employing a metal nitrate and a catalytic amount of p-toluenesulfonic acid in acetone. An exclusive ortho-selectivity was observed with excellent yields. A variety of metal nitrates were used to obtain o-nitrophenols exclusively in good to excellent yields. The use of p-toluenesulfonic acid is key for the selectivity observed. 相似文献