全文获取类型
收费全文 | 1535篇 |
免费 | 86篇 |
出版年
2023年 | 14篇 |
2022年 | 24篇 |
2021年 | 38篇 |
2020年 | 35篇 |
2019年 | 36篇 |
2018年 | 54篇 |
2017年 | 51篇 |
2016年 | 65篇 |
2015年 | 79篇 |
2014年 | 92篇 |
2013年 | 119篇 |
2012年 | 131篇 |
2011年 | 126篇 |
2010年 | 57篇 |
2009年 | 48篇 |
2008年 | 75篇 |
2007年 | 71篇 |
2006年 | 65篇 |
2005年 | 60篇 |
2004年 | 57篇 |
2003年 | 49篇 |
2002年 | 45篇 |
2001年 | 37篇 |
2000年 | 26篇 |
1999年 | 15篇 |
1998年 | 9篇 |
1997年 | 7篇 |
1996年 | 7篇 |
1995年 | 8篇 |
1993年 | 3篇 |
1992年 | 9篇 |
1991年 | 8篇 |
1990年 | 4篇 |
1989年 | 11篇 |
1988年 | 8篇 |
1987年 | 3篇 |
1986年 | 8篇 |
1985年 | 6篇 |
1984年 | 6篇 |
1983年 | 3篇 |
1979年 | 4篇 |
1978年 | 3篇 |
1976年 | 3篇 |
1974年 | 3篇 |
1970年 | 4篇 |
1968年 | 3篇 |
1967年 | 2篇 |
1955年 | 2篇 |
1933年 | 3篇 |
1931年 | 2篇 |
排序方式: 共有1621条查询结果,搜索用时 46 毫秒
11.
Paiva R. P. Munita C. J. S. Cunha I. I. L. Romano J. Alonso C. D. 《Biological trace element research》1990,(1):231-242
Two nuclear techniques, Energy-Dispersive X-Ray Fluorescence Analysis (EDXRF) and Instrumental Neutron Activation Analysis (INAA), were used to analyze aerosol samples collected in the city of São Paulo, Brazil. Na, Cl, Mn, V, Al, Sm, Mo, W, La, As, Br, Sb, K, Ba, Se, Th, Cr, Rb, Ca, Fe, Ce, and Sc were determined by INAA, and Al, Si, P, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Ga, As, Se, Br, Rb, Sr, Hg, and Pb were determined by EDXRF. A preliminary identification of the main source of the atmospheric aerosol was performed based on enrichment factor and correlation coefficient calculations.
相似文献12.
Serum-free culture of enriched mouse anterior and ventral prostatic epithelial cells in collagen gel
Timothy Turner Howard A. Bern Peter Young Gerald R. Cunha 《In vitro cellular & developmental biology. Plant》1990,26(7):722-730
Summary Sustained growth of mouse ventral and anterior prostatic epithelial cells embedded within collagen gel matrix was achieved
in a serum-free medium composed of Dulbecco's modified Eagle's medium and Ham's F12 medium, 1∶1 (vol/vol), supplemented with
bovine serum albumin fraction V, epidermal growth factor, transferrin, cholera toxin, prolactin, 5α-dihydrotestosterone, cortisol,
putrescine, fibroblast growth factor, and a trace element mixture. Three-dimensional growth of prostatic epithelial cells
occurred inside the collagen gel matrix. This serum-free medium allowed cell growth greater than sevenfold over 10 d in culture.
Tissue recombination and cell culture techniques were integrated to demonstrate that cultured cells retained prostatic characteristics.
Following 10 d of culture, epithelial colonies from mouse ventral and anterior prostatic epithelial cell cultures were isolated
and combined with rat fetal urogenital sinus mesenchyme and grown for 4 wk under the renal capsule of intact athymic male
mice. These tissue recombinants showed distinctive prostatic histologic characteristic (alveoli and ducts lined with cuboidal
or columnar epithelium surrounded by stroma). When histologic sections of recombinants were stained with the Hoechst 33258,
epithelial cells of mouse origin were distinguishable from stromal cells of rat origin.
Aided by grants CA-05388 and CA-09041 from the National Institutes of Health, Bethesda, MD, and by M. A. R. C. fellowship
GM08730 to T. T. 相似文献
13.
14.
Ana Cristina Gomes da Cunha Manuel Fernandes Ferreira 《Plant Cell, Tissue and Organ Culture》1996,47(1):1-8
The effects of plant growth regulators (PGR) on calli induction, morphogenesis and somatic embryogenesis of flax were studied. The organogenic and callus formation capacity were assessed for different types of source explants. Root and shoot explants were equally good material for calli production but the former produced calli without shoot regeneration capacity. Under the experimental conditions tested, 2,4-dichlorophenoxyacetic acid (2,4-D) + zeatin was the most efficient PGR combination on calli induction and biomass production. The calli were green but with no rhizogenic capacity. In contrast, and at similar concentrations, indole-3-butyric acid (IBA) + kinetin induced white or pale green friable calli with a good root regeneration capacity (60%). A factorial experiment with different combinations of 2,4-D + zeatin + gibberellic acid (GA3) levels revealed that the direction of explant differentiation was determined by specific PGR interactions and concentrations. The results from these experiments revealed that the morphogenetic pathway (shoot versus root differentiation) can be manipulated on flax explants by raising the 2,4-D level from 0.05 to 3.2 mg l?1 in the induction medium. The induction and development of somatic embryos from flax explants was possible in a range of 2,4-D + zeatin concentrations surrounding 0.4 mg l?1 2,4-D and 1.6 mg l?1 zeatin, the most efficient growth regulator combination. 相似文献
15.
Marcello Franco Eduardo Bagagli Marino Cunha Luiz Gastão Chamma Denise Fecchio 《Mycopathologia》1996,135(1):13-19
We investigated the occurrence of antigenic and biochemical variability among Paracoccidioides brasiliensis antigen batches prepared according to the same protocol. Initially (experiment #1), we analyzed two antigen lots of two human isolates (Bt1 & Bt2), cultured in two media (PYG: bactopeptone, yeast extract, glucose; MMM: McVeigh & Morton medium) in SDS-PAGE and in two immunological tests (imunodiffusion-ID and footpad swelling test-FPT). Afterwards (experiment #2), we compared the antigenic profile of three antigen batches from three human isolates (Bt1, Bt2 & Bt3) by two-dimensional immunoelectrophoresis (2 D-IEP) against a reference system for P. brasiliensis antigens. In experiment #1, there were important intra- and inter-strain antigenic differences between batches of the fungal isolates cultured on both media. The block titration of the antigen batches for the immunological tests revealed correlation between protein concentration and biological activity in ID and no correlation in FPT. In experiment #2, the reference system for P. brasiliensis showed 26 antigen peaks. There were important differences between batches prepared from the same isolate and between batches from different isolates. Our data suggested the occurrence of instability in the synthesis of antigenic components by a same P. brasiliensis isolate, under controlled incubation conditions. 相似文献
16.
Rodrigo A. Cunha E. Milusheva †E. S. Vizi J. A. Ribeiro A. M. Sebastião 《Journal of neurochemistry》1994,63(1):207-214
Abstract: The modulation by adenosine analogues and endogenous adenosine of the electrically evoked release of [3H]acetylcholine ([3H]ACh) was compared in subslices of the three areas of the rat hippocampus (CA1, CA3, and dentate gyrus). The mixed A1/A2 agonist 2-chloroadenosine (CADO; 2–10 µM) inhibited, in a concentration-dependent manner, the release of [3H]ACh from the three hippocampal areas, being more potent in the CA1 and CA3 areas than in the dentate gyrus. The inhibitory effect of CADO (5 µM) on [3H]ACh release was prevented by the A1 antagonist 1,3-dipropyl-8-cyclopentylxanthine (DPCPX; 50 nM) in the three hippocampal areas and was converted in an excitatory effect in the CA3 and dentate gyrus areas. The A2A agonist CGS-21680 (30 nM) produced a greater increase of the evoked release of [3H]ACh in the CA3 than in the dentate gyrus areas, whereas no consistent effect was found in the CA1 area or in the whole hippocampal slice. The excitatory effect of CGS-21680 (30 nM) in the CA3 area was prevented by the adenosine receptor antagonist 3,7-dimethyl-1-propargylxanthine (10 µM). Both adenosine deaminase (2 U/ml) and DPCPX (250 nM) increased the evoked release of [3H]ACh in the CA1 and CA3 areas but not in the dentate gyrus. The amplitude of the effect of DPCPX and adenosine deaminase was similar in the CA1 area, but in the CA3 area DPCPX produced a greater effect than adenosine deaminase. It is concluded that the electrically evoked release of [3H]ACh in the three areas of the rat hippocampus can be differentially modulated by adenosine. In the CA1 area, only A1 inhibitory receptors modulate ACh release, whereas in the CA3 area, both A2A excitatory and A1 inhibitory adenosine receptors modulate ACh release. In the dentate gyrus, both A1 inhibitory and A2A excitatory adenosine receptors are present, but endogenous adenosine does not activate them. 相似文献
17.
Amanda dos Santos Marina Tenório Botelho Willian Reina Joviano Vicente Gomes José Roberto Machado Cunha da Silva Gisela de Aragão Umbuzeiro 《Invertebrate Biology》2023,142(1):e12394
Hemocytes are circulating blood cells that play a crucial function in amphipods and other crustacean immune systems. The hemocytes of the marine tropical amphipod Parhyale hawaiensis have been used for the evaluation of DNA damage and micronuclei, but they have not been characterized in the scientific literature. The aim of this study was to describe the hemolymph cells of P. hawaiensis and study their phagocytotic activity. Basic dyes were used to differentiate the cell types and the presence of lipids. The total hemocyte counts (THCs) and the proportion and sizes of the hemocyte types were determined. Hemolymph was exposed to Escherichia coli for verification of the presence of phagocytosis. Three cell types, all containing lipids, were identified in P. hawaiensis: granulocytes (oval shape, 13.4 × 7.6 μm), semi-granulocytes (oval shape, 14.1 × 7.2 μm), and hyalinocytes (round shape, 9.6 × 7.2 μm). Those three cell types were found in different percentages in males (64.8%, 31.1%, and 4.2%) and females (70.1%, 28.2%, and 1.7%). THCs for males were 9007 ± 3800 cells per individual and 4695 ± 1892 cells per individual for females. The cells of E. coli were phagocytized by the hemocytes. Our findings increased the knowledge of hemocytes in P. hawaiensis and is a step forward in using hemocyte-based immune responses as an endpoint in ecotoxicology. 相似文献
18.
19.
20.
Environmental gradients in a southern Europe estuarine system: Ria de Aveiro,Portugal implications for soft bottom macrofauna colonization 总被引:4,自引:0,他引:4
Four seasonal sampling surveys were carried out between December 1985 and September 1986 in Canal de Mira (Ria de Aveiro,
Portugal). A total of 40 sampling stations, distributed over 13 transects, was used. Salinity, temperature, dissolved oxygen
and pH of the water mass were measured. Sediment temperature, and salinity and pH of interstitial water were determined. Sediment
variables also included granulometric composition and organic matter contents. Bottom macrofauna samples were collected at
each station.
Ordination (PCA and MDS) and classification of the sampling stations were performed, using the physicochemical and the biological
data sets separately. Average linkage cluster analysis using the unweighted paired-group method, arithmetic averages, was
used for both sets of data.
With a salinity range from 35.1‰ to 0.0‰, Canal de Mira behaves like a tidally and seasonally poikilohaline estuary. Water
temperature (8.5–24.7°C) decreased along the channel towards its inner part during the cold season; an inverse and more pronounced
trend was observed during the hot season. Dissolved oxygen contents was generally high during the day (50% to 240% saturation).
Oversaturation was observed throughout the growing season, with peaks in areas with large amounts of rooted vegetation. The
pH values, largely correlated with dissolved oxygen, ranged from 6.8 to 8.9. Four types of sediment were present in Canal
de Mira, medium and muddy sands being dominant.
Two major gradients were identified: (i) a typical longitudinal estuarine gradient, associated with distance from the mouth,
representing physicochemical variables such as tidal amplitude, salinity and temperature; this gradient was accompanied by
an upstream increase in dominance; the community composition changes were mainly related to salinity; (ii) a lateral gradient,
related to current velocity, depth and sediment composition; the subtidal community had a comparatively low species richness
and abundance. Groups of stations could be recognized along the environmental gradients. Benthic community changes, however,
appeared to be gradual rather than marked by abrupt transitions. 相似文献