全文获取类型
收费全文 | 282853篇 |
免费 | 30620篇 |
国内免费 | 352篇 |
出版年
2016年 | 3216篇 |
2015年 | 4499篇 |
2014年 | 5095篇 |
2013年 | 7766篇 |
2012年 | 8370篇 |
2011年 | 8609篇 |
2010年 | 5676篇 |
2009年 | 5243篇 |
2008年 | 7707篇 |
2007年 | 7831篇 |
2006年 | 7455篇 |
2005年 | 7176篇 |
2004年 | 7043篇 |
2003年 | 6824篇 |
2002年 | 6615篇 |
2001年 | 11916篇 |
2000年 | 11966篇 |
1999年 | 9427篇 |
1998年 | 3364篇 |
1997年 | 3590篇 |
1996年 | 3466篇 |
1995年 | 3194篇 |
1994年 | 3178篇 |
1993年 | 3171篇 |
1992年 | 8031篇 |
1991年 | 7999篇 |
1990年 | 7657篇 |
1989年 | 7612篇 |
1988年 | 6968篇 |
1987年 | 6730篇 |
1986年 | 6134篇 |
1985年 | 6347篇 |
1984年 | 5286篇 |
1983年 | 4475篇 |
1982年 | 3479篇 |
1981年 | 3228篇 |
1980年 | 3009篇 |
1979年 | 5080篇 |
1978年 | 3904篇 |
1977年 | 3815篇 |
1976年 | 3505篇 |
1975年 | 3874篇 |
1974年 | 4263篇 |
1973年 | 4174篇 |
1972年 | 3754篇 |
1971年 | 3494篇 |
1970年 | 3145篇 |
1969年 | 3054篇 |
1968年 | 2789篇 |
1967年 | 2417篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
beta, a novel repetitive DNA element associated with tRNA genes in the pathogenic yeast Candida albicans 总被引:2,自引:0,他引:2
We have identified a novel 399 bp repetitive DNA element (which we designate beta ) 9 bp upstream of a seryl-tRNACAG gene in the genome of Candida albicans . There are two copies of the seryl-tRNACAG gene, one on each homologue of chromosome VI, and the beta element is found upstream of one copy of the gene in C. albicans strain 2005E. The beta element is not present upstream of either copy of the seryl-tRNACAG gene in eight other laboratory strains of C. albicans tested, but was detected in this location in several fresh clinical isolates. Southern blot analysis indicated that there are approximately eight copies of the beta element per diploid C. albicans genome and that it is a mobile element, being present on at least two different chromosomes. Three unique genomic DNA clones containing the beta element were isolated from strain 2005E; in each case, a different tRNA gene was found immediately adjacent to the beta element. Three new tRNA genes from C. albicans have thus been identified: tRNAAsp , tRNAAla and tRNAIle . The beta element shows no significant sequence homology to other known prokaryotic or eukaryotic repetitive elements, although an 8 bp repeat at the 3' end of the element is identical to that of the Ty3 retrotransposable element of Saccharomyces cerevisiae . We propose that the beta element is a solo long terminal repeat (LTR) sequence of a Ty3/gypsy-like transposable element in C. albicans that is closely associated with tRNA genes. 相似文献
82.
83.
The 1,3-regiospecific lipase from Candida deformanscatalysed the esterification of oleic acid and propanediol in biphasic aqueous/lipid medium without organic solvent. The highest conversion of oleic acid into 1,2-propanediol ester was 74% in 24 h with 6.25 mol/l 1,2-propanediol and 0.08 mol/l oleic acid, and produced 100% monoester. The esterification of 1,3-propanediol converted up to 98% of oleic acid into esters in 24 h (with 7.5 mol/l 1,3-propanediol and 0.08 mol/l oleic acid) and formed 35-90% monoester depending on 1,3-propanediol initial concentration (2.5-10 mol/l). 相似文献
84.
85.
Anthony E. Kincaid Kathryn F. Hudson Matthew W. Richey Jason C. Bartz 《Journal of virology》2012,86(23):12731-12740
Prion infection and pathogenesis are dependent on the agent crossing an epithelial barrier to gain access to the recipient nervous system. Several routes of infection have been identified, but the mechanism(s) and timing of in vivo prion transport across an epithelium have not been determined. The hamster model of nasal cavity infection was used to determine the temporal and spatial parameters of prion-infected brain homogenate uptake following inhalation and to test the hypothesis that prions cross the nasal mucosa via M cells. A small drop of infected or uninfected brain homogenate was placed below each nostril, where it was immediately inhaled into the nasal cavity. Regularly spaced tissue sections through the entire extent of the nasal cavity were processed immunohistochemically to identify brain homogenate and the disease-associated isoform of the prion protein (PrPd). Infected or uninfected brain homogenate was identified adhering to M cells, passing between cells of the nasal mucosa, and within lymphatic vessels of the nasal cavity at all time points examined. PrPd was identified within a limited number of M cells 15 to 180 min following inoculation, but not in the adjacent nasal mucosa-associated lymphoid tissue (NALT). While these results support M cell transport of prions, larger amounts of infected brain homogenate were transported paracellularly across the respiratory, olfactory, and follicle-associated epithelia of the nasal cavity. These results indicate that prions can immediately cross the nasal mucosa via multiple routes and quickly enter lymphatics, where they can spread systemically via lymph draining the nasal cavity. 相似文献
86.
87.
M. Ehrlich R. Trittler F. D. Daschner K. Kümmerer 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》2001,755(1-2)
A sensitive and rapid HPLC-assay for determining the new oxazolidinone antibiotic linezolid in serum and urine is described. HPLC-integrated sample preparation permits the direct injection of serum and urine samples without any pre-treatment. The in-line extraction technique is realized by switching automatically from the extraction column to the analytical column. After the matrix has passed the extraction column the retained analyte will be quantitatively transferred to the analytical column where separation by isocratic HPLC will be performed. Linezolid is detected according to its absorption maximum at 260 nm. The quantification limits are estimated to be 0.3 and 0.5 μg/ml in serum and urine samples, respectively. The described procedure allows sample clean-up and determination of the antibiotic within 20 min, thereby facilitating drug-monitoring in clinical routine. 相似文献
88.
Female lifespan and reproduction, in terms of numberof larvae produced, of the soil-dwelling predatorymite Lasioseius fimetorum Karg (Acari:Podocinidae) fed on mould mites (Tyrophagusputrescentiae [Schrank] [Acarina: Acaridae]) wereinvestigated by laboratory experiments at 20 °C,as were the mite's consumption rates of various prey.After a preoviposition period of 10.7 days, L.fimetorum produced progeny at a daily rate of 0.7.The oviposition period lasted 23.6 days and a total of19.4 progeny were produced per female. Females livedfor 38.6 days. Eggs of the Collembola Isotomurusspp. (Collembola: Isotomidae) were consumed in thelargest amount by L. fimetorum followed by mouldmite nymphs, larvae and pupae of thrips (Frankliniella occidentalis [Pergande] [Thysanoptera:Thripidae]), eggs of the Collembola Micrisotomaspp. (Collembola: Isotomidae), Isotomurus spp.nymphs and sciarid larvae (Bradysia pauperaTuomikoski and B. tritici (Coquillet) [Diptera:Sciaridae]). Immature drain flies (Psychoda spp.[Diptera: Psychodidae]) were not consumed by L.fimetorum. The suitability of L. fimetorum forbiological control of glasshouse pests withsoil-dwelling stages is discussed in comparison withanother predatory mite Hypoaspis miles Berlese(Acarina: Hypoaspididae). 相似文献
89.
An ATP-Sensitive K+ Current that Regulates Progression Through Early G1 Phase of the Cell Cycle in MCF-7 Human Breast Cancer Cells 总被引:4,自引:0,他引:4
Whole-cell recordings were used to identify in MCF-7 human breast cancer cells the ion current(s) required for progression
through G1 phase of the cell cycle. Macroscopic current-voltage curves were fitted by the sum of three currents, including
linear hyperpolarized, linear depolarized and outwardly rectifying currents. Both linear currents, but not the outwardly rectifying
current, were increased by 1 μm intracellular Ca2+ and blocked by 2 mm intracellular ATP. When tested at concentrations previously shown to inhibit proliferation by 50%, linogliride, glibenclamide
and quinidine inhibited the linear hyperpolarized current, and quinidine and linogliride inhibited the linear depolarized
current; none of these agents affected the outwardly rectifying current. In contrast, tetraethylammonium completely inhibited
the outwardly rectifying current, but did not inhibit either linear current. Changing the bath solution to symmetric K+ shifted the reversal potential of the linear hyperpolarized current from near the K+ equilibrium potential (−84 mV) to −4 mV. Arrest of the cell cycle in early G1 by quinidine was associated with significantly
smaller linear hyperpolarized currents, without a change in the linear depolarized or outwardly rectifying currents, but this
reduction was not observed with arrest by lovastatin at a site ≈6 hr later in G1. The linear hyperpolarized current was significantly
larger in ras-transformed than in untransformed cells. We conclude that the linear hyperpolarized current is an ATP-sensitive K+ current required for progression of MCF-7 cells through G1 phase.
Received: 22 January 1999/Revised: 11 May 1999 相似文献
90.