全文获取类型
收费全文 | 332778篇 |
免费 | 37193篇 |
国内免费 | 188篇 |
出版年
2018年 | 2838篇 |
2017年 | 2698篇 |
2016年 | 3869篇 |
2015年 | 5326篇 |
2014年 | 6229篇 |
2013年 | 8749篇 |
2012年 | 9985篇 |
2011年 | 9960篇 |
2010年 | 6796篇 |
2009年 | 6133篇 |
2008年 | 8853篇 |
2007年 | 9296篇 |
2006年 | 8593篇 |
2005年 | 8281篇 |
2004年 | 8004篇 |
2003年 | 7763篇 |
2002年 | 7767篇 |
2001年 | 18141篇 |
2000年 | 18376篇 |
1999年 | 14099篇 |
1998年 | 4227篇 |
1997年 | 4495篇 |
1996年 | 4301篇 |
1995年 | 4006篇 |
1994年 | 3943篇 |
1993年 | 3781篇 |
1992年 | 11484篇 |
1991年 | 11124篇 |
1990年 | 10675篇 |
1989年 | 10244篇 |
1988年 | 9480篇 |
1987年 | 8840篇 |
1986年 | 8079篇 |
1985年 | 7958篇 |
1984年 | 6390篇 |
1983年 | 5561篇 |
1982年 | 4103篇 |
1981年 | 3591篇 |
1980年 | 3355篇 |
1979年 | 6109篇 |
1978年 | 4570篇 |
1977年 | 4125篇 |
1976年 | 3760篇 |
1975年 | 4331篇 |
1974年 | 4497篇 |
1973年 | 4389篇 |
1972年 | 4090篇 |
1971年 | 3498篇 |
1970年 | 3168篇 |
1969年 | 2968篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
D. C. Coleman R. V. Anderson C. V. Cole E. T. Elliott L. Woods M. K. Campion 《Microbial ecology》1977,4(4):373-380
Flows of biomass and respiratory carbon were studied in a series of propylene-oxide sterilized soil microcosms. One-half of the microcosms received three pulsed additions of 200 ppm glucose-carbon to mimic rhizosphere carbon inputs. Biotic variables were: bacteria (Pseudomonas) alone, or amoebae (Acanthamoeba) and nematodes (Mesodiplogaster) singly, or both combined in the presence of bacteria.Over the 24-day experiment, respiration was significantly higher in the microcosms containing the bacterial grazers. Biomass accumulation by amoebae was significantly higher than that by nematodes. The nematodes respired up to 30-fold more CO2 per unit biomass than did amoebae. Similar amounts of carbon flowed into both respiratory and biomass carbon in microcosms with fauna, compared with the bacteria-alone microcosms. However, partitioning of available carbon by the microfauna varied considerably, with little biomass production and relatively more CO2-C produced in the nematode-containing microcosms. The amoebae, in contrast, allocated more carbon to tissue production (about 40% assimilation efficiency) and correspondingly less to CO2. 相似文献
982.
983.
984.
K Maskos 《Acta biochimica Polonica》1985,32(3):235-250
The copper (II)-inosine system in water-DMSO solutions was investigated as a function of pH and the molar ratio between the ligand and copper(II) ion by the EPR, NMR, CD and visible absorption spectrometric methods. It was concluded that a simple M.[-N]L copper(II)-inosine 1:1 complex is formed over the pH range 1.4-5.0, while M.[-N]L2 complexes are present in the solutions of pH 5.0-6.2. From pH 6.2 to 7.8 a diamagnetic, hydroxybridged complex M2.(OH)2.[-N]L4 dominates. At pH values of 7.8-9.2 an insoluble, oxybridged species (M.O.[-N]L)n is formed in addition to the soluble paramagnetic M.[-N-1)L4 complex. Above pH 9.1 the nitrogenbridged polymeric complex (M.[-N-1].M[-N-7] )n is formed which is stable up to pH 12.5, and above pH 12.5 the only species found is the M.[-OH]L2 chelate complex in which inosine is coordinated to copper through the two ionized hydroxyl groups. 相似文献
985.
In view of the importance of impedance plethysmography requirements are formulated for a modern impedance measuring device basing on a long experience with this method of measurement. The principle mode of action of the measuring equipment and the pneumatics with the timing element are described. A number of recordings is shown to illustrate the universality of the measuring equipment. 相似文献
986.
987.
988.
989.
Of the 1,972 deaths investigated by autopsy at the Los Angeles County Hospital in 1951, 64 were attributed to bronchogenic carcinoma. However, in some of these cases the protocols did not contain sufficient data to substantiate the diagnosis or the tissue specimens were not conclusive evidence. Although the survey left no doubt that the lung was the most common site of primary carcinoma in the series studied, a wider application of the findings is limited by the facts that patients with bronchogenic carcinoma are more likely than others to die in hospitals and that selection of cases for autopsy depends on the interest of the physician and the consent of the patient's survivors. 相似文献
990.
Free and derivatized aglycones and parent ascarosides of Ascaris lumbricoides and A. columnaris (Nematoda) were isolated by thin-layer and gas chromatography and analyzed by mass spectrometry and polarimetry. Results for monol aglycones confirmed previous chain-length assignments and the location of the l-hydroxyl group at C-2. The major monols of even carbon number possessed a methyl branch on the penultimate carbon (ω ? 1). Diol alycones were entirely unbranched homologues, mainly 31 and 33 carbons long, and had hydroxyl groups on C-2 and C-(ω ? 1). These aglycones were truly symmetrical, for they were optically inactive with the center bearing the glycone in diol ascaroside (C-2), being mostly or entirely the l configuration. Three major features of ascaroside structure—chain length composition of the aglycones, molecular weight of the unusual glycone (a dideoxyhexose), the kind and position of acyl groups—were clearly discernible in the spectra of intact ascarosides. 相似文献