全文获取类型
收费全文 | 2644篇 |
免费 | 105篇 |
国内免费 | 83篇 |
出版年
2023年 | 40篇 |
2022年 | 25篇 |
2021年 | 25篇 |
2020年 | 46篇 |
2019年 | 67篇 |
2018年 | 70篇 |
2017年 | 46篇 |
2016年 | 39篇 |
2015年 | 45篇 |
2014年 | 108篇 |
2013年 | 175篇 |
2012年 | 88篇 |
2011年 | 130篇 |
2010年 | 98篇 |
2009年 | 107篇 |
2008年 | 132篇 |
2007年 | 114篇 |
2006年 | 97篇 |
2005年 | 87篇 |
2004年 | 67篇 |
2003年 | 78篇 |
2002年 | 63篇 |
2001年 | 37篇 |
2000年 | 37篇 |
1999年 | 36篇 |
1998年 | 29篇 |
1997年 | 24篇 |
1996年 | 23篇 |
1995年 | 21篇 |
1994年 | 17篇 |
1993年 | 17篇 |
1992年 | 13篇 |
1991年 | 13篇 |
1990年 | 15篇 |
1988年 | 11篇 |
1987年 | 10篇 |
1985年 | 45篇 |
1984年 | 86篇 |
1983年 | 51篇 |
1982年 | 70篇 |
1981年 | 87篇 |
1980年 | 64篇 |
1979年 | 60篇 |
1978年 | 50篇 |
1977年 | 50篇 |
1976年 | 43篇 |
1975年 | 53篇 |
1974年 | 42篇 |
1973年 | 47篇 |
1971年 | 9篇 |
排序方式: 共有2832条查询结果,搜索用时 15 毫秒
1.
《Nucleosides, nucleotides & nucleic acids》2013,32(5-8):1039-1040
Abstract Crown ether 4 as a receptor core for protonated primary amines such as amino acids has been synthesized and incorporated into oligodeoxynucleotides as dangling ends. 相似文献
2.
Victor F. Medina Peter M. Jeffers Steven L. Larson Waleska Perez 《International journal of phytoremediation》2000,2(4):287-295
Bleach treatment of plants was studied as a simple alternative to axenic tissue cultures for demonstrating phytodegradation of aqueous and gas-phase environmental contaminants. Parrotfeather (Myriophyllum aquaticum), spinach (Spinacia oleracea), and wheat (Triticum aestivum) were exposed to 0.525% NaC10 solutions for 15 s, then rinsed in deionized water. Plate counts indicated that 97 to 100% of viable bacteria were removed from parrotfeather and spinach. Transformation rates for 2,4,6-trinitrotoluene (TNT) by bleached and untreated parrotfeather were virtually identical. Similarly, treated and untreated spinach, wheat heads, and wheat leaves removed methyl bromide (MeBr) from air at the same rates. However, wheat root with attendant adhering soil was rendered inactive by bleach treatment. Parrotfeather roots examined by dissecting microscope and by electron microscope showed no significant damage caused by bleach treatment. 相似文献
3.
Phytochemical analysis of dried twigs of Marsdenia roylei (family Asclepiadaceae) has resulted in the isolation of a trisaccharide, maryal, and a diglycoside, rolinose. Their structures were determined as O-beta-D-oleandropyranosyl-(1-->4)-O-beta-D-digitoxopyranosyl++ +-(1-->4)-D- cymaral and ethyl O-beta-D-oleandropyranosyl-(1-->4)-O-3-O-methyl-6-deoxy-beta-D- allopyranoside, respectively, by chemical degradation and spectroscopic methods. 相似文献
4.
Koichi Inoue Akiko Yamaguchi Megumi Wada Yoshihiro Yoshimura Tsunehisa Makino Hiroyuki Nakazawa 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》2001,765(2):3469-126
Due to the ubiquity of epoxy resin compounds and their potential role in increasing the risk for reproductive dysfunction and cancer, the need for an assessment of human exposure is urgent. Therefore, we developed a method for measuring bisphenol A (BPA) and bisphenol A diglycidyl ether (BADGE) metabolites in human blood samples using high-performance liquid chromatography–electrospray ionization mass spectrometry (LC–MS). Human blood samples were processed using enzymatic deconjugation of the glucuronides followed by a novel sample preparation procedure using a solid-phase-cartridge column. This selective analytical method permits rapid detection of the metabolites, free BPA and a hydrolysis product of BADGE (BADGE-4OH) with detection limits in the low nanogram per milliliter range (0.1 ng ml−1 of BPA and 0.5 ng ml−1 of BADGE-4OH). The sample extraction was achieved by Oasis HLB column on gradient elution. The recoveries of BPA and BADGE-4OH added to human plasma samples were above 70.0% with a standard deviation of less than 5.0%. This selective, sensitive and accurate method will assist in elucidating potential associations between human exposure to epoxy-based compounds and adverse health effects. 相似文献
5.
Ranganathan Santhanam 《Inorganica chimica acta》2008,361(2):473-478
A novel method of preparation of hexahydroaluminate complexes M3AlH6 (M = Li, Na or K) from the corresponding alkali metal hydride and tetrahydroaluminate has been explored, using dimethyl ether (Me2O) as a solvent at near-ambient temperatures. The results are compared with those obtained using a recently established mechanochemical approach. Characterization of the products by powder X-ray diffraction revealed M3AlH6 to be formed in high yield for M = Li and Na, but not for M = K. The attempted preparation of Li2NaAlH6 and Li2KAlH6 was unsuccessful. 相似文献
6.
Three specimens of Ayapana triplinervis (Vahl) R.M. King & H. Rob from Reunion Island (Indian Ocean) collected at two distant locations (North of the island; samples 1 and 2, South of the island; sample 3), in different growth phases (flowering; samples 1 and 3, vegetative; sample 2) were investigated for their leaf essential oil composition. This study reports the chemical character of this species on the island and investigates the relationship between essential oil composition, developmental stage and geographic location. Analysis by GC–FID and GC–MS enabled us to identify and quantify a total of 39 constituents accounting for 97.1–98.0% of the oils. The three essential oil samples, all obtained by hydrodistillation, showed a high percentage of the aromatic compound thymohydroquinone dimethyl ether (89.9–92.8%). All other minor components remained more or less unchanged both qualitatively and quantitatively with respect to the stage of growth. On the contrary, variations were observed with geographic distribution. The geographical variation of the chemical composition of the volatile oil of A. triplinervis from several sites in the world is also briefly discussed. 相似文献
7.
The effect of methyl bromide (MB) was tested on active and anhydrobiotic Aphelenchus avenae. A. avenae was induced into anhydrobiosis by three different techniques. Both active and anhydrobiotic nematodes were subjected to 3,000 μ1 MB/liter air for 14 periods from 0 to 82 h. Anhydrobiotic nematodes were more resistant to fumigation than active nematodes, regardless of the technique used to induce anhydrobiosis. The percent survival decreased with increasing MB exposures (μ1 MB × h). For an LD₉₅ of 45,000-54,000 μ1/1 × h were required for active nematodes and >279,000 μ1/1 × h for anhydrobiotic nematodes. 相似文献
8.
Identification of hydrogen selenide and other volatile selenols by derivatization with 1-fluoro-2,4-dinitrobenzene 总被引:2,自引:0,他引:2
A procedure is described for the trapping and identification of hydrogen selenide and methyl selenol ( CH3SeH ). The volatile selenols were generated by reducing selenious acid or dimethyldiselenide with Zn dust and hydrochloric acid under a stream of nitrogen and passing into a trapping solution composed of 50 mM 1-fluoro-2,4-dinitrobenzene plus 83 mM sodium bicarbonate in 67% dimethylformamide:33% water. The selenols react rapidly to form stable dinitrophenyl (DNP) selenoethers that can be extracted into benzene; these are easily identified by TLC, HPLC, or mass spectrometry. Hydrogen selenide is trapped in 90-99% yield, primarily as the di-DNP- monoselenide with a trace of di-DNP- diselenide . 相似文献
9.
E. M. Karalova L. H. Hakobyan M. R. Tatoyan K. T. Sahakyan 《Biotechnic & histochemistry》2013,88(5):309-312
ABSTRACTWe present an easy test for rapid visualization of viral DNA assemblies in infected cell cytoplasm. We selected the best stains for nuclear staining: Nile blue A, Bismarck brown, gallocyanin chrome alum, methyl green pyronin and azure II. None of the staining techniques is fluorescent, which facilitates their use in everyday experiments. Methyl green is most promising for routine detection of viral DNA assemblies in the cytoplasm; the procedure enables ready detection of viral DNA accumulation in the cytoplasm. 相似文献
10.
K Folkers T Kubiak H Stepien N Sakura 《Biochemical and biophysical research communications》1980,97(2):601-606
A new approach to the study of the molecular arrangements of proteins in membranes is described. Irradiation with visible light of native erythrocytes or washed erythrocyte membranes suspended in buffers containing a) riboflavin, fluorescein or fluorescein coupled to dextran and b) 3H-labelled tryptophan resulted in incorporation of radioactivity into the membrane proteins. Polyacrylamide gel electrophoresis of solubilized membranes followed by radioactivity measurements of the separated membrane proteins revealed that in native erythrocytes the protein components known to be located at the exterior cell surface, Band 3 and the major sialoglycoproteins became specifically labelled, whereas in washed lysed cells all of the major membrane proteins were labelled. 相似文献