全文获取类型
收费全文 | 579118篇 |
免费 | 59637篇 |
国内免费 | 421篇 |
专业分类
639176篇 |
出版年
2018年 | 10266篇 |
2017年 | 10101篇 |
2016年 | 10293篇 |
2015年 | 8961篇 |
2014年 | 10494篇 |
2013年 | 15256篇 |
2012年 | 18871篇 |
2011年 | 23345篇 |
2010年 | 16565篇 |
2009年 | 15508篇 |
2008年 | 19954篇 |
2007年 | 21868篇 |
2006年 | 14710篇 |
2005年 | 14952篇 |
2004年 | 14473篇 |
2003年 | 14064篇 |
2002年 | 13496篇 |
2001年 | 28449篇 |
2000年 | 28368篇 |
1999年 | 21974篇 |
1998年 | 6725篇 |
1997年 | 7314篇 |
1996年 | 6747篇 |
1995年 | 6208篇 |
1994年 | 5983篇 |
1993年 | 5983篇 |
1992年 | 17051篇 |
1991年 | 16306篇 |
1990年 | 15700篇 |
1989年 | 15221篇 |
1988年 | 13920篇 |
1987年 | 12942篇 |
1986年 | 12040篇 |
1985年 | 11812篇 |
1984年 | 9667篇 |
1983年 | 8094篇 |
1982年 | 6005篇 |
1981年 | 5372篇 |
1980年 | 5095篇 |
1979年 | 8940篇 |
1978年 | 6809篇 |
1977年 | 6272篇 |
1976年 | 5645篇 |
1975年 | 6243篇 |
1974年 | 6758篇 |
1973年 | 6540篇 |
1972年 | 6497篇 |
1971年 | 5882篇 |
1970年 | 4684篇 |
1969年 | 4399篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The microbial degradation of morpholine 总被引:5,自引:1,他引:4
Morpholine can be completely degraded microbiologically, and two organisms have been isolated, each capable of growth in a simple mineral salts medium with morpholine as the sole source of carbon, nitrogen and energy. Excess nitrogen is liberated as ammonia. The enzymes responsible for the oxidation of morpholine are inducible and, in organism Mor G, will also oxidize piperidine, piperazine and pyrrolidine, which are not growth substrates. Ethanolamine is a likely intermediate, though the metabolic steps in morpholine degradation do not give rise solely to acetyl-CoA. After a period of acclimation, a laboratory scale activated sludge plant effectively removed morpholine over the long period it was operated; the sludge was also capable of nitrification. The possible effects of other chemicals in trade wastes containing morpholine on nitrification and morpholine oxidation are described. 相似文献
992.
Alexander V. Kirdyanov Eugene A. Vaganov Malcolm K. Hughes 《Trees - Structure and Function》2007,21(1):37-44
We propose a technique for separating the climatic signal which is contained in two tree-ring parameters widely used in dendroclimatology.
The method is based on the removal of the relationship between tree-ring width (TRW) and maximum latewood density (MXD) observed
for narrow tree rings from high latitudes. The new technique is tested on data from three larch stands located along the northern
timberline in Eurasia. Correlations were calculated between the temperatures of pentads (five consecutive days), TRW chronologies
and MXD chronologies calculated according to the standard and proposed methods. The analysis confirms the great importance
of summer temperature for tree radial growth and tree-ring formation. TRW is positively correlated with the temperature of
four to eight pentads (depending on the region) at the beginning of the growth season, but MXD as obtained by the standard
technique is correlated with temperature over a much longer period. For maximum density series from which the relationship
between MXD and TRW has been removed (MXD′), there is a clear correlation with temperatures in the second part of the growing
season. These results are consistent with the known dynamics of tree-ring growth in high latitudes and mechanisms of tree-ring
formation. 相似文献
993.
994.
995.
996.
Ya. O. Loginov G. G. Khudaigulov S. P. Chetverikov A. I. Melent’ev O. N. Loginov 《Applied Biochemistry and Microbiology》2011,47(3):311-314
Highly viscous polysaccharide (250–350 kDa) of an alginate nature with a predominance of α-L-guluronic acid (M/G = 0.22) was
obtained from Azotobacter vinelandi. The yield of polysaccharide was 20.5 ± 0.5 g/l when cultured in a medium containing molasses at a viscosity of the cultural
liquid of over 30000 cSt. The biopolymer is stable at pH 4.0–9.0 in a wide temperature range and well soluble in highly mineralized
water; it retains a high viscosity level and can be used in the petroleum industry for enhanced oil recovery. 相似文献
997.
I. A. Parfenov T. A. Revina P. P. Pashkovsky N. L. Radyukina T. A. Valueva 《Applied Biochemistry and Microbiology》2011,47(4):361-365
Product of polymerase chain reaction designated as PKPIJ-B was isolated after amplification from genomic DNA of potato (Solarium tuberosum L., Zhukov Jubilee cultivar) using the designed primers. Nucleotide sequence of PKPIJ-B was determined and amino acid sequence of protein was restored. Analysis of this sequence has allowed us to suggest that
isolated gene fragment encodes chymotrypsin and trypsin inhibitor protein (PKCI-23 potato Kunitz-type chymotrypsin inhibitor)
of potato tubers. 相似文献
998.
The synthesis of some monocyclic beta-lactams (monobactams) by the Staudinger reaction using D-glucosamine propanedithioacetal as chiral auxiliary is reported. The influence of several radicals at C3, C4, and C1' (sugar moiety) as well as other structural aspects are considered in relation to the antielastase activity. 相似文献
999.
1000.
Cokun Kse Evren Terzi S. Nami Kartal 《International biodeterioration & biodegradation》2009,63(6):727-731
This study evaluated the relative ability of various combinations of copper sulfate with either boric acid or calcium-precipitating agent, N′-N-(1, 8-naphthalyl) hydroxylamine (NHA-Na), to inhibit fungal degradation and attack by Formosan subterranean termites (Coptotermes formosanus Shiraki). Wood specimens were treated with either 1%, 0.5%, or 0.1% concentrations of copper sulfate, boric acid, NHA-Na, copper sulfate + boric acid, or copper sulfate + NHA-Na mixtures. Treated specimens were subjected to laboratory decay-resistance tests by using petri dishes inoculated with the Basidiomycetes fungi Tyromyces palustris and Trametes versicolor for 12 weeks. Treated wood specimens were also subjected to termite-resistance tests under laboratory conditions. Increased efficacy of copper sulfate against the brown-rot fungus T. palustris was observed when either boric acid or NHA-Na was added. The most effective treatments against the fungi tested were NHA-Na only treatments at 1% and 0.5% concentration levels. Boric acid treatments were not able to protect wood against decay after leaching because of excessive leaching of boron. Similar results were obtained in termite-resistance tests in comparison with decay-resistance tests. These results indicate that the efficacy of the treatments in preventing fungal and termite attack is a function of the type of preservative. 相似文献