全文获取类型
收费全文 | 1433篇 |
免费 | 116篇 |
专业分类
1549篇 |
出版年
2021年 | 14篇 |
2020年 | 12篇 |
2019年 | 11篇 |
2018年 | 27篇 |
2016年 | 26篇 |
2015年 | 33篇 |
2014年 | 50篇 |
2013年 | 45篇 |
2012年 | 64篇 |
2011年 | 62篇 |
2010年 | 37篇 |
2009年 | 50篇 |
2008年 | 60篇 |
2007年 | 43篇 |
2006年 | 50篇 |
2005年 | 62篇 |
2004年 | 36篇 |
2003年 | 40篇 |
2002年 | 40篇 |
2001年 | 33篇 |
2000年 | 43篇 |
1999年 | 35篇 |
1998年 | 17篇 |
1997年 | 19篇 |
1996年 | 16篇 |
1994年 | 15篇 |
1993年 | 12篇 |
1992年 | 32篇 |
1991年 | 38篇 |
1990年 | 30篇 |
1989年 | 23篇 |
1988年 | 28篇 |
1987年 | 24篇 |
1986年 | 19篇 |
1985年 | 18篇 |
1984年 | 22篇 |
1982年 | 18篇 |
1981年 | 14篇 |
1980年 | 20篇 |
1979年 | 20篇 |
1978年 | 18篇 |
1977年 | 25篇 |
1976年 | 12篇 |
1975年 | 16篇 |
1974年 | 19篇 |
1973年 | 18篇 |
1972年 | 20篇 |
1971年 | 20篇 |
1969年 | 15篇 |
1968年 | 11篇 |
排序方式: 共有1549条查询结果,搜索用时 15 毫秒
21.
A non-invasive assay for measurement of oxytocin (OT) and vasopressin (AVP) in primates would enable researchers to study the relationship between the endocrine system and behavior without disturbing potentially endangered animals in their natural habitats. In order to test whether or not OT specifically would be measurable in the urine of a primate, 10 microCi of tritium-labeled OT were injected into the peripheral blood supply of four adult male common marmosets (Callithrix jacchus), with continuous urinary collection over 48 h. When urine was processed by HPLC separation and beta counting for radioactive clearance, the label was present in all samples in the fraction where OT elutes. Large amounts of OT were also seen in a fraction other than that containing the OT standard, indicating that OT is measurable but that it also undergoes substantial metabolic breakdown. In a second experiment, we isolated six common marmosets for 48 h and then exposed them to social contact to evaluate the effect of changing social stimuli on endogenous urinary measurement of both OT and AVP. Both were measured after HPLC separation to isolate the intact molecule and also to control for cross-reactivity with metabolites in subsequent RIA. Cortisol was also measured to objectively evaluate the stress response. A priori assumptions were that urinary OT and AVP would be lower during a period of isolation and higher during periods of social contact. These assumptions were met, leading us to conclude that peripheral OT and AVP are measurable via urinary assay and that such an assay is a valid means of evaluating social condition in this species. 相似文献
22.
Summary An analysis was made of the effects of different sampling and extraction techniques on the amounts and pattern of monoterpenoids isolated from needles of Norway spruce. The following isolation and analysis procedure was finally adopted: liquid nitrogen-cooled needles were pulverized by a microdismembrator, extracted with pentane overnight at 2°–3°C and concentrated to a volume not less than 3 ml/g fresh weight on a Vigreux column. The crude extract was injected splitless (with solvent split) onto a cold programmed temperature vaporized (PTV) precolumn of a gas chromatograph and the vaporizable compounds heated to a capillary column. This method was tested for production of artefacts and quantitative extraction and applied to needles of eleven 80-year-old spruce trees. 相似文献
23.
To avoid interpretative problems due to restriction fragment length polymorphisms, the monosomy 6 mutant cell line BM19.7 was employed to establish a molecular map of the human major histocompatibility (HLA) complex in the A2,B13,Bw4,DRw6,DRw52,DQw1,DPw2 haplotype. Results were obtained mainly by field-inversion gel electrophoresis and Southern blotting techniques. The map extends to 4800 kb and includes the HLA complex with a length of 4200 kb. Five HTF islands could be positioned on the map. The class I region has a size of about 2000 kb and includes nonclassical HLA class I genes, some of which must be localized within 200 kb telomeric of HLA-A. A new class I gene, cda12, distinct from HLA-A, HLA-B, or HLA-C, has been localized within 50 kb from HLA-A. The class I region contains a gap of about 500 kb, just telomeric of HLA-C, in which further class I genes could not be detected. The class II region has a size of 1000 kb, which is separated from the class I region by about 1200 kb. The 5' end of the HLA-B gene is situated centromeric, giving an orientation opposite to that of the TNFA and TNFB loci. The estimated length of the HLA complex correlates well with its size determined cytogenetically using mutant cell lines with interstitial deletions. 相似文献
24.
R Ziegler L A Willingham D L Engler K J Tolman D Bellows D J Van Der Horst G M Yepiz-Plascencia J H Law 《European journal of biochemistry》1999,261(1):285-290
A new type of insect lipoprotein was isolated from the hemolymph of the female cochineal insect Dactylopius confusus. The lipoprotein from the cochineal insect hemolymph was found to have a relative molecular mass of 450 000. It contains 48% lipid, mostly diacylglycerol, phospholipids and hydrocarbons. The protein moiety of the lipoprotein consists of two apoproteins of approximately 25 and 22 kDa, both of which are glycosylated. Both apolipoproteins are also found free in the hemolymph, unassociated with any lipid. Purified cochineal apolipoproteins can combine with Manduca sexta lipophorin, if injected together with adipokinetic hormone into M. sexta. This could indicate that the cochineal lipoprotein can function as a lipid shuttle similar to lipophorins of other insects, and that the cochineal insect apolipoproteins have an overall structure similar to insect apolipophorin-III. 相似文献
25.
Ohne Zusammenfassung 相似文献
26.
Hubert Ziegler 《Planta》1963,60(1):41-45
Zusammenfassung Das im Phloem nicht wanderfähige45Calcium wird aus wachsenden Früchten vonCucurbita maxima durch den Fruchtstiel abtransportiert, und zwar mit einer Geschwindigkeit, die eine Normaldiffusion nicht zu erzielen vermag. Es wird dies als Indiz für einen Rückstrom im Xylem betrachtet.Mit 2 TextabbildungenHerrn Professor Dr.Arthur Pisek zum 70. Geburtstag gewidmet. 相似文献
27.
28.
Effects of common atopy-associated amino acid substitutions in the IL-4 receptor alpha chain on IL-4 induced phenotypes 总被引:3,自引:1,他引:3
Franjkovic I Gessner A König I Kissel K Bohnert A Hartung A Ohly A Ziegler A Hackstein H Bein G 《Immunogenetics》2005,56(11):808-817
The human IL-4 receptor alpha chain gene (IL4R) is highly polymorphic and controversial reports have been published with respect to the association of different single nucleotide polymorphisms (SNPs) with atopy markers. Here we analyzed the functional and associational relevance of common IL4R coding SNPs. Transfection of B cell lines expressing the IL-4R variant V75+R576 did not result in enhanced IL-4 induced CD23 expression compared to cell lines expressing the wild type IL-4R alpha chain. Transfection of the IL-4R variant P503 into a murine T cell line did not influence IL-4 induced T-cell proliferation compared to wild type constructs. Analysis of six IL4R coding SNPs (I75V, E400A, C431R, S436L, S503P, Q576R) and common haplotypes (frequency 0.05%) in blood donors (n=300) did not indicate a significant association with elevated serum IgE level. Moreover, the most informative IL4R coding SNPs (I75V, C431R, Q576R) and related two- and three-point haplotypes (frequency 0.05%) were analyzed in a second, extended group of blood donors (n=689). Again, no significant association with elevated serum IgE was detectable. We conclude that common coding SNPs in the IL4R gene are unlikely to contribute significantly to increased IgE levels and variations outside the coding region may influence atopy susceptibility. 相似文献
29.
Natali AN Carniel EL Pavan PG Bourauel C Ziegler A Keilig L 《Journal of biomechanics》2007,40(8):1701-1708
The paper pertains to the analysis of the biomechanical behaviour of the periodontal ligament (PDL) by using a combined experimental and numerical approach. Experimental analysis provides information about a two-rooted pig premolar tooth in its socket with regard to morphological configuration and deformational response. The numerical analysis developed for the present investigation adopts a specific anisotropic hyperelastic formulation, accounting for tissue structural arrangement. The parameters to be adopted for the PDL constitutive model are evaluated with reference to data deducted from experimental in vitro tests on different specimens taken from literature. According to morphometric data relieved, solid models are provided as basis for the development of numerical models that adopt the constitutive formulation proposed. A reciprocal validation of experimental and numerical data allows for the evaluation of reliability of results obtained. The work is intended as preliminary investigation to study the correlation between mechanical status of PDL and induction to cellular activity in orthodontic treatments. 相似文献
30.
Ziegler TR Luo M Estívariz CF Moore DA Sitaraman SV Hao L Bazargan N Klapproth JM Tian J Galloway JR Leader LM Jones DP Gewirtz AT 《American journal of physiology. Regulatory, integrative and comparative physiology》2008,294(2):R402-R410
Gut barrier dysfunction may occur in short bowel syndrome (SBS). We hypothesized that systemic exposure to flagellin and lipopolysaccharide (LPS) in SBS might regulate specific immune responses. We analyzed serial serum samples obtained from parenteral nutrition (PN)-dependent patients with SBS versus non-SBS control serum. Serum from 23 adult SBS patients was obtained at baseline and 4, 8, 12, 16, 20, and 24 wk in a trial of modified diet with or without growth hormone. Control serum was obtained from 48 healthy adults and 37 adults requiring PN during critical illness. Serum flagellin was detected by an ELISA recognizing an array of gram-negative flagellins, and LPS was detected by limulus assay. Serum flagellin- and LPS-specific immunoglobulin levels (IgM, IgA, and IgG) were determined by ELISA. Serum flagellin and LPS were undetectable in control subjects. In contrast, serum flagellin, LPS, or both were detected in 14 SBS patients (61%) during one or more time points [flagellin alone, 5/23 (22%); LPS alone, 6/23 (26%); or flagellin + LPS, 3/23 (13%)]. Flagellin-specific serum IgM, IgA, and IgG levels were markedly increased in SBS patients compared with both control populations and remained elevated during the 6-mo study period. LPS-specific IgA was significantly higher in SBS patients compared with healthy controls; LPS-specific IgM, IgA, and IgG levels each decreased over time in association with PN weaning. We conclude that adults with PN-dependent SBS are systemically exposed to flagellin and LPS, presumably from the gut lumen. This likely regulates innate and adaptive immune responses to these specific bacterial products. 相似文献