全文获取类型
收费全文 | 530篇 |
免费 | 96篇 |
国内免费 | 32篇 |
专业分类
658篇 |
出版年
2023年 | 6篇 |
2022年 | 10篇 |
2021年 | 7篇 |
2020年 | 9篇 |
2019年 | 9篇 |
2018年 | 5篇 |
2017年 | 8篇 |
2016年 | 14篇 |
2015年 | 13篇 |
2014年 | 16篇 |
2013年 | 28篇 |
2012年 | 37篇 |
2011年 | 35篇 |
2010年 | 25篇 |
2009年 | 24篇 |
2008年 | 32篇 |
2007年 | 23篇 |
2006年 | 19篇 |
2005年 | 14篇 |
2004年 | 26篇 |
2003年 | 18篇 |
2002年 | 22篇 |
2001年 | 13篇 |
2000年 | 19篇 |
1999年 | 20篇 |
1998年 | 8篇 |
1997年 | 8篇 |
1996年 | 5篇 |
1995年 | 8篇 |
1994年 | 10篇 |
1993年 | 8篇 |
1992年 | 10篇 |
1991年 | 14篇 |
1990年 | 8篇 |
1989年 | 13篇 |
1988年 | 10篇 |
1987年 | 3篇 |
1986年 | 9篇 |
1985年 | 7篇 |
1984年 | 6篇 |
1983年 | 7篇 |
1982年 | 5篇 |
1981年 | 5篇 |
1979年 | 5篇 |
1978年 | 5篇 |
1977年 | 3篇 |
1974年 | 5篇 |
1973年 | 5篇 |
1970年 | 4篇 |
1967年 | 4篇 |
排序方式: 共有658条查询结果,搜索用时 15 毫秒
621.
Histology and cell wall biochemistry of stone cells in the physical defence of conifers against insects 下载免费PDF全文
622.
Michiel?M?Zandbelt Judith?Vogelzangs Leo?BA?van de Putte Walther?J?van Venrooij Frank?HJ?van den HoogenEmail author 《Arthritis research & therapy》2003,6(1):R33
The presence of anti-α-fodrin autoantibodies has been reported to be a highly specific and sensitive test for the diagnosis of Sjögren's syndrome (SjS). We looked (in Nijmegen) for anti-α-fodrin, anti-Ro60, and anti-La autoantibodies in a cohort of 51 patients with rheumatic diseases (primary SjS [21], secondary SjS [6], rheumatoid arthritis [RA] [12], systemic lupus erythematosus [SLE] [6], and scleroderma [6]) and in 28 healthy subjects, using ELISA, immunoblotting, and immunoprecipitation. The same samples were analyzed with an alternative anti-α-fodrin ELISA in Hanover. The Nijmegen ELISA of the sera from primary SjS showed sensitivities of 43% and 48% for IgA- and IgG-type anti-α-fodrin antibodies, respectively. The Hanover ELISA showed sensitivities of 38% and 10% for IgA- and IgG-type anti-α-fodrin antibodies, respectively. The ELISAs for α-fodrin showed six (Nijmegen) and four (Hanover) anti-α-fodrin-positive RA sera. IgA and IgG anti-fodrin antibodies were also present in four patients with secondary SjS. The sensitivities of Ro60 and La-antibodies in the Nijmegen ELISA were 67% and 62%, respectively. Unlike anti-α-fodrin antibodies, all anti-Ro60 and anti-La positive sera could be confirmed by immunoblotting or RNA immunoprecipitation. Thus, anti-Ro and anti-La autoantibodies were more sensitive than anti-α-fodrin autoantibodies in ELISA and were more frequently confirmed by other techniques. Anti-La antibodies appear to be more disease-specific than anti-α-fodrin antibodies, which are also found in RA sera. Therefore, the measurement of anti-α-fodrin autoantibodies does not add much to the diagnosis of Sjögren's syndrome. 相似文献
623.
624.
Two populations of Anadara senilis were sampled periodicallyin a lagoon of Senegal. Spatfall occurs in summer during therainy season. Population density decreases from about 50, 000.m2,two months after spatfall, down to 6, 750 one year later and750 after 28 months. The average growth, measured on the surfaceof the shell, following the umbo rim axis is 0.8 mm per month.The main reduction in growth rate occurs in winter and endsby the deposition of a growth ring. A second growth reductiontakes place during the rainy season and sometimes ends by aweak growth ring. The microgrowth increments are conspicuousand widest during spring equinox. They are not directly relatedto the tidal cycle, but it was impossible to determine if theyhave a tidal or a daily periodicity. (Received 11 February 1990; accepted 16 July 1993) 相似文献
625.
Determinations were made of carbohydrates in hemolymph collected from adult female mosquitoes (Anopheles stephensi). First the hemolymph was fractionated by extraction and precipitation procedures, after which qualitative and quantitative determinations of carbohydrates were made by thin layer chromatography. The most abundant sugars found in the hemolymph were glucose and trehalose, though maltose, glucuronic acid, and inositol could be found after the mosquitoes took blood meals. After the mosquitoes ingested a noninfected blood meal, their hemolymph sugar levels rose almost 4-fold. There was less of an increase following a blood meal infected with the rodent malaria parasite, Plasmodium berghei. Depletion of sugars in the hemolymph of infected mosquitoes may result from direct utilization of sugar by the malaria parasite developing within the mosquito. 相似文献
626.
The Effects of Silicon Supplementation on Cucumber Fruit: Changes in Surface Characteristics 总被引:3,自引:0,他引:3
Addition of silicate to hydroponic nutrient media has been shownto increase resistance of cucumber to powdery mildew. As a sideeffect of this treatment, the fruit surface developed an unusualdull appearance, or bloom. The effects of silicate supplementationon cucumber fruit were observed using scanning and transmissionelectron microscopy, energy-dispersive X-ray analysis, and colourimetricassays. Changes in the fruit trichome morphology occurred: trichomesfrom + Si fruit had a coarse outer appearance compared to -Si fruit where the trichomes were smooth. X-ray mapping showedhigh Si content in trichomes but not in the surrounding epidermisor fleshy mesocarp and endocarp tissues. Sections through theepidermal layer reveal that the silica is restricted to thetrichomes, primarily in the epicuticular wax.Copyright 1993,1999 Academic Press Cucumber, Cucumis sativus L., fruit, silica, energy dispersive X-ray analysis, trichomes 相似文献
627.
A cross-sectional demographic analysis of the entire baboon population of the Amboseli basin of southern Kenya was undertaken
to complement the lon-gitudinal, intensive studies of a subpopulation. The present survey documented the extent and persistence
of the influx of anubis baboons into the predominantly cynocephalus community and provided another example of the nonrandom
dispersal patterns of cercopithecine males. In addition, the survey confirmed continued demographic stability of the basinwide
baboon population and even growth in groups that had access to better feeding conditions, despite decline of the baboons'
preferred habitat and expansion of human activities into wildlife areas. Conflicts with activities of humans, however, indicate
that the present well-being of the Amboseli baboon population may be short-lived. 相似文献
628.
Presented here is a stable isotope dilution technique for determining cortisol production rate (CPR). The method involves extraction and derivatization of cortisol isoforms from serum (0.5 ml), separation of derivatives by gas chromatography, and detection by using negative ion chemical ionization mass spectrometry. This method provides 50-100-fold greater sensitivity than positive ion mass spectrometry and allows for estimations of cortisol production rate with the use of small amounts of pooled serum, even in the presence of high concentrations of lipophilic contaminants. The area under the curve for the total selected ion chromatogram of fluoroacyl derivatives of cortisol (d0, m/z 782) and deuterated cortisol (d3, m/z 785) were used to determine the isotopic dilution ratio in three types of samples: 1) standards: d0/d3 ratios ranging from 1 to 8%; 2) controls: d3-cortisol added to serum with known cortisol concentration; 3) subjects: 24-h pooled serum samples (q 30 min over 24 h) from healthy children (male 10-13 years; female 7-11 years) receiving continuous infusions of d3-cortisol at 2-4% of their estimated CPR. Recovery after the solid phase extraction and derivatization process was >90%, as determined by thin-layer chromatography. Expected versus measured ratios for d3/d0 in standards and serum controls were highly correlated (r2(standard) = 0.99; r2(control) = 0.99) over a wide range of d3-cortisol enrichment (1.0-10.0%). Mean 24-h CPRs were 4.8 +/- 0.6 mg/m2/24 h (mean +/- SEM, n = 7) in male children and 4.4 +/- 0.5 mg/m2/24 h in female children (n = 4). These CPR values are lower than those derived by radio tracer methods, but are in agreement with previous isotopic dilution studies. This technique is an important tool for assessing CPRs in a wide range of disease states affecting cortisol production. 相似文献
629.
The influence of shrimps on turbidity was examined in laboratory and field experiments. Palaemonetes varians in the laboratory
stimulated populations of both rotifers and Anabaena, which was the main cause of increased turbidity. In field experiments,
P. varians increased and Neomysis integer decreased turbidity. In feeding trials P. varians took cladocerans and culicids
in preference to copepods. It is considered that shrimps are likely to be important predators of cladocerans in shallow, coastal
waterbodies and result in phytoplankton blooms, with reduced water transparency.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
630.