全文获取类型
收费全文 | 89947篇 |
免费 | 16905篇 |
国内免费 | 9171篇 |
专业分类
化学 | 61482篇 |
晶体学 | 916篇 |
力学 | 5747篇 |
综合类 | 514篇 |
数学 | 10106篇 |
物理学 | 37258篇 |
出版年
2024年 | 344篇 |
2023年 | 2043篇 |
2022年 | 3298篇 |
2021年 | 3389篇 |
2020年 | 3929篇 |
2019年 | 3513篇 |
2018年 | 3219篇 |
2017年 | 2872篇 |
2016年 | 4583篇 |
2015年 | 4371篇 |
2014年 | 5322篇 |
2013年 | 6769篇 |
2012年 | 8211篇 |
2011年 | 8406篇 |
2010年 | 5557篇 |
2009年 | 5383篇 |
2008年 | 5784篇 |
2007年 | 5069篇 |
2006年 | 4765篇 |
2005年 | 3825篇 |
2004年 | 2944篇 |
2003年 | 2294篇 |
2002年 | 2108篇 |
2001年 | 1817篇 |
2000年 | 1605篇 |
1999年 | 1840篇 |
1998年 | 1591篇 |
1997年 | 1576篇 |
1996年 | 1563篇 |
1995年 | 1322篇 |
1994年 | 1150篇 |
1993年 | 996篇 |
1992年 | 859篇 |
1991年 | 783篇 |
1990年 | 643篇 |
1989年 | 501篇 |
1988年 | 370篇 |
1987年 | 308篇 |
1986年 | 323篇 |
1985年 | 261篇 |
1984年 | 151篇 |
1983年 | 117篇 |
1982年 | 100篇 |
1981年 | 57篇 |
1980年 | 42篇 |
1979年 | 15篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1957年 | 31篇 |
1922年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 5 毫秒
991.
Zhanglin Liu Dong Tian Fei Shen Lulu Long Yanzong Zhang Gang Yang Yongmei Zeng Jing Zhang Jinsong He Ying Zhu Shihuai Deng 《中国化学快报》1990,30(12):2221-2224
Four distinct biochars were employed to remove three typical pollutants, meanwhile, path analysis, a multi-statistical regression method, was performed to elucidate the dominant factors of biochar adsorption. This work can provide a new insight to prepare a targeted biochar as adsorbents. 相似文献
992.
Jian X. Gao Jian C. Wang Chong L. Song T. Liu Tian D. Hu Ya N. Xie J. Zhang G. Wang H. Yang 《Journal of solution chemistry》2006,35(1):113-119
NMR spectroscopy was used to show that the symmetry of the crown ether bis(C6) is increased by an increase of the alkali metal
cation radius. The EXAFS spectrum demonstrates that a seven oxygen atom coordinated configuration is present in the bis(C6)/Cs+/NPME system, where NPME denotes o-nitrophenylmethyl ether. The seventh oxygen in this complex, besides the six crown ether oxygens of bis(C6), may come either
from a H2O molecule or an NO3− ion. 相似文献
993.
Crystal structures of new nitronyl nitroxide derivatives 1, 2 and 3 were determined with X‐ray diffraction analysis: 1, monoclinic, C2/c, a = 1.2404(5) nm, b = 0.9730(5) um, c = 2.7049(10) ran, β = 98.189(15)°, V = 3.2315(24) nm3, Z = 8; 2, or‐thorhombic, Pbca, a = 0.61262(2) nm, b = 1.11426(6) nm, c = 2.30543(13) nm, V = 1.57373(13) nm3, Z = 4; 3, monoclinic, P2(1)/n, a=0.64253(4) nm, b=2.55003(17) nm, c = 1.15497(6) nm, β = 95.000(3)°, V = 1.8852(2) nm3, Z = 4. Their magnetic properties were measured with SQUID and analyzed based on their crystal structures with simple singlet‐triplet, modified one dimensional antiferromagnetic chain and modified singlet‐triplet models respectively: 1, J/kb= ?2.5 K; 2, J/kb = 7.8 K, θ = 2.8 K; 3, J/kb = ?0.96 K, θ = 0.21 K. 相似文献
994.
A new capillary electrophoresis procedure with field-enhanced stacking concentration for the analysis of strychnine and brucine is established. After optimization of the separation and concentration conditions, the two alkaloids can be separated within 5 min and quantified with high sensitivity (The detection limits were 1.0 ng mL(-1) for strychnine and 1.4 ng mL(-1) for brucine). The method was useful for qualitative and quantitative analysis of strychnine and brucine in Strychnos nux-vomica L with recovery of 105.1% for strychnine and 98.4% for brucine. 相似文献
995.
By the use of differential scanning calorimetry (DSC), a new method to measure the wax content of crude oil has been developed. In this paper, the wax content of a crude oil is proposed and proved to be the Q (total thermal effect of wax precipitation in sample) ratio of the crude oil and its corresponding wax obtained by using standard acetone method, i.e. Qoil/Qwax. For the 14 studied crude oils with the wax content ranging from 1 to 27 wt.%, the wax contents determined by the presented method are in good agreement with those determined by standard acetone method, with an absolute average deviation of only 0.82 wt.%. This method has an advantage over reported DSC methods in which the exact dissolution or precipitation enthalpy of wax is a must. It is also found that the wax contents determined by either of the two methods show good linear relationship with the total thermal effect Qoil, with the correlation coefficients over 0.96. According to the empirical correlations, the wax content of a crude oil can be easily determined by using the DSC total thermal effect Qoil. In addition and more significantly, the new method can be applied to improve the accuracy in determining the amount of precipitated wax in a waxy crude oil at different temperatures. 相似文献
996.
A new high-performance liquid chromatographic (HPLC) method for measuring low molecular weight (LMW) thiol-containing compounds, including cysteine (CysH), glutathione (GSH), N-acetylcysteine (Nac), penicillamine (PA), and 2-mercaptoethanol (2-ME), has been developed by using 5-methyl-(2-(m-iodoacetylaminophenyl)benzoxazole (MIPBO) as fluorescence-labeling reagent. The derivatization and separation conditions have been investigated in detail. Detection limits ranging from 3.5 to 15.0 fmol were achieved for the thiols investigated in a 16 min separation with detection wavelengths 310 and 375 nm for the excitation and emission, respectively. The utility of the proposed method has been validated by measuring CysH in human urine samples. 相似文献
997.
Dispersion of MoO3, NiO, ZnO on rutile TiO2 with low specific surface area was studied with Mercury Porosimeter, SEM, XPS and Ammonia Extraction method. The dispersion thresholds of MoO3, NiO, ZnO on three rutile TiO2 carriers were obtained with XPS, and com-pared with those on anatase TiO2 with high specific surf are area. Ammonia Extraction method was used to identify the surface oxide species interarting with support surface in different strength and it was found that the proportions of oxides that can not be extracted by ammonia extraction are different for MoO3, NiO and ZnO which are supported on rutile TiO2. 相似文献
998.
999.
采用XAFS方法研究浸渍法制备并于低温焙烧的CuO/γ-Al2O3催化剂的局域结构.对于CuO负载量小于单层分散阈值的CuO/γ-Al2O3(0.4 mmol/100 m2),结果表明,CuO物种是以层状分散的孤立原子簇存在于γ-Al2O3载体表面,其第一近邻Cu-O配位环境的结构与晶态CuO的相似,键长和配位数分别为0.195 nm和4.对于CuO负载量等于单层分散阈值的CuO/γ-Al2O3(0.8 mmol/100 m2),已有少量的CuO纳米颗粒生成.对于CuO负载量大于单层分散阈值的CuO/γ-Al2O3(1.2 mmol/100 m2),其结构与多晶CuO的相近.基于CuO在γ-Al2O3载体上的三种不同分散状态的结构特点,我们提出了CuO/γ-Al2O3催化剂的结构模型. 相似文献
1000.
Ma B Chen Y Hao H Wu M Wang B Lv H Zhang G 《Colloids and surfaces. B, Biointerfaces》2005,41(2-3):197-201
Under the background of algae removal and growth inhibition by ultrasonic irradiation, the effects of ultrasonic irradiation on removal of Microcystis, the concentration variation of microcystins (MC) produced by Microcystis in Microcystis suspension, and sonochemical degradation of microcystins in water, were studied in the paper. The results showed that ultrasonic irradiation could efficiently inhibit the growth of Microcystis, and ultrasonic irradiation shorter than 5 min would not introduce the increase of microcystins dissolved in Microcystis suspension simultaneity. Also, microcystins dissolved in Microcystis suspension would not increase as ultrasonic power increasing. Further research showed that microcystins were effectively degraded in ultrasonic fields. After 20 min ultrasonic irradiation at 150 kHz and 30 W, the removal rate of microcystins reached 70%. 相似文献