全文获取类型
收费全文 | 12913篇 |
免费 | 980篇 |
国内免费 | 1篇 |
出版年
2023年 | 54篇 |
2022年 | 52篇 |
2021年 | 149篇 |
2020年 | 123篇 |
2019年 | 137篇 |
2018年 | 229篇 |
2017年 | 279篇 |
2016年 | 328篇 |
2015年 | 427篇 |
2014年 | 498篇 |
2013年 | 680篇 |
2012年 | 997篇 |
2011年 | 1057篇 |
2010年 | 566篇 |
2009年 | 426篇 |
2008年 | 786篇 |
2007年 | 862篇 |
2006年 | 745篇 |
2005年 | 654篇 |
2004年 | 607篇 |
2003年 | 645篇 |
2002年 | 578篇 |
2001年 | 308篇 |
2000年 | 348篇 |
1999年 | 170篇 |
1998年 | 131篇 |
1997年 | 105篇 |
1996年 | 123篇 |
1995年 | 99篇 |
1994年 | 110篇 |
1993年 | 98篇 |
1992年 | 83篇 |
1991年 | 87篇 |
1990年 | 86篇 |
1989年 | 78篇 |
1988年 | 65篇 |
1987年 | 55篇 |
1986年 | 75篇 |
1985年 | 76篇 |
1984年 | 88篇 |
1983年 | 83篇 |
1982年 | 79篇 |
1981年 | 83篇 |
1980年 | 76篇 |
1979年 | 64篇 |
1978年 | 65篇 |
1977年 | 62篇 |
1976年 | 45篇 |
1974年 | 29篇 |
1973年 | 35篇 |
排序方式: 共有10000条查询结果,搜索用时 250 毫秒
71.
Leif Asbjørn Vøllestad 《Ecography》1985,8(2):88-92
In this paper I investigate the resource partitioning of roach Rutilus rutilus and bleak Alburnus alburnus in two eutrophic lakes in SE Norway. Zooplankton was the preferred food item for both species during summer, whereas blue-green algae dominated the diet in September/October. There was no diet overlap in May, with the roach feeding mainly on detritus and the bleak feeding on surface insects. During summer the diet overlap increased, reaching high values in autumn. Habitat overlap was close to unity in spring and early summer. Coinciding with increasing diet overlap during summer and autumn the overlap in habitat decreased. 相似文献
72.
Jørgen Johansen Anna L. Kleinhaus 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1985,157(4):491-497
Properties of divalent cation potentials carried by either Sr2+ or Ca2+ ions in Na+-free, TEA-Ringer solution were characterized in identified neurons of two species of leeches (Macrobdella and Haementeria). In Macrobdella, the overshoot of the potentials varied logarithmically with [Sr2+]0 (28.5 mV per 10-fold change). The overshoot, Vmax, and duration of the potentials increased with increasing divalent cation concentration and saturated at about 20 to 30 mM [Sr2+]0. The Vmax, amplitude, and duration of the potentials were reversibly blocked by Co2+ and Mn2+. The block by Mn2+ could be well-fitted by a reverse Langmuir-curve with an apparent KI of 100 micromolar. The local anesthetic procaine also reversibly inhibited the Vmax and duration of the potentials. The inhibition was greater at alkaline pH suggesting that procaine blocks the calcium channel from inside the membrane. The identified leech neurons examined in Macrobdella varied considerably in their ability to sustain somatic divalent cation potentials. Stimulation of T cells and most motoneurons produced no or only weak potentials, whereas stimulation of Retzius, N, Nut, and AP cells evoked overshooting potentials of several seconds' duration. Stimulation of the ALG cell of Haementeria in normal Ringer solution evoked a slowly-rising, purely Ca2+-dependent potential of approximately 100 ms duration. This response was TTX-resistant, unaffected by complete removal of Na+ from the Ringer solution, and abolished by 1 mM Mn2+. The overshoot varied logarithmically with a slope of 28 mV/decade change in [Ca2+]0. 相似文献
73.
Animal community structure as a function of stream size 总被引:1,自引:1,他引:0
Christer Brönmark Jan Herrmann Björn Malmqvist Christian Otto Per Sjöström 《Hydrobiologia》1984,112(1):73-79
The species-area relationship of the island biogeography theory was calculated for macroinvertebrates in 22 coastal, adjacent streams. A z-value of 0.19 was obtained. The low z-value was probably a consequence of the short distances between streams as well as high dispersal rates. In addition, a cluster analysis based on the dissimilarity of species assemblages showed that stream size was of prime importance in categorizing the streams. To a smaller extent water quality affected the community structure in the streams. 相似文献
74.
Jan Dahmén Torbjörn Frejd Göran Magnusson Ghazi Noori Anne-Sofie Carlström 《Carbohydrate research》1984,125(2):237-245
The applicability of 2-bromoethyl glycosides in carbohydrate synthesis is demonstrated by the synthesis of glycosides of alpha-L-Fuc-(1----2)-D-Gal and beta-D-Gal-(1----4)-D-GlcNAc. The bromoethyl aglycon was transformed into the methoxycarbonylethylthioethyl spacer, which allowed coupling of the sugars to proteins (BSA and KLH). 相似文献
75.
Lars Olof Björn 《Physiologia plantarum》1984,60(3):369-372
Experiments by several authors on the effects of polarized light on phytochromemediated responses in fern gametophytes and in the green alga Mougeotia have earlier been interpreted as showing that the transition moment of phytochrome in the Pr form is parallel to the plasmalemma, but perpendicular to the plasmalemma for the Pfr form of phytochrome. It is now shown that the experimental results can be interpreted differently, and that they are also consistent with a chromophore rotation of about 30° (instead of 90°), as found for immobilized phytochrome molecules in vitro. Thus there is no evidence for a rotation of the whole phytochrome protein. For the gametophyte of Adiantum it is calculated that the Pr transition moment is inclined 17° to the plasmalemma, and the Pfr transition moment ca 50°, corresponding to an in vivo chromophore rotation of ca 33°; however, these values are very approximate. 相似文献
76.
Photosynthesis and nitrogen utilization in exponentially growing nitrogen-limited cultures of Lemna gibba 总被引:2,自引:0,他引:2
The photosynthetic performance and nitrogen utilization of Lemna gibba L. G3 adapted to limited nitrogen supply was studied. The plants were adapted to two levels of nitrogen limitation where the nitrogen addition rates were calculated to sustain relative growth rates (RGR) of 0.15 day?1 and 0.25 day?1, respectively. The photosynthetic performance of these cultures was compared to nitrogen-sufficient cultures with an average RGR of 0.32 day?1. Plants transferred from nitrogen-sufficient conditions attained RGR values corresponding to the nitrogen addition rates after 6 to 10 days. Light-saturated net photosynthesis declined during adaptation according to the drop in growth rate, and a concomitant decrease in the respiration rate was recorded. The efficiency of net photosynthesis on a dry weight basis increased with increased nitrogen supply, whereas it was the same in all cultures when expressed on a chlorophyll basis. The light compensation point was unaffected by the nitrogen regime. Limited nitrogen supply resulted in an increased proportion of dry matter in the roots, which led to decreased leaf area ratios. The net assimilation rates also decreased, but not to the same extent as the leaf area ratios. Growth-limiting amounts of nitrogen were added to the cultures once daily, and the net influx of N was higher than the requirement for N, also in adapted cultures with a steady growth rate. This resulted in transient, periodic fluctuations in the NO3?, NH4+ and amino acid pools. Also the rates of NO3? reduction and NH4+ assimilation fluctuated as did the amino acid assimilation which paralleled NH4+ assimilation. The role of flux rates over the plasmalemma and tonoplast for control of nitrogen assimilation rates are discussed. 相似文献
77.
Conidiation in Alternaria cichorii Nattras is reversibly stimulated by near ultraviolet radiation (NUV, ca 313 nm) and inhibited by blue light (ca 450 nm) and seems to be a mycochrome-mediated process. After induction with plane-polarized NUV, blue light polarized perpendicularly to the NUV was more effective in counteracting the induction than was blue light polarized parallel to the NUV. From this the conclusions are drawn that (a) both the blue-absorbing component (presumably a flavo-protein) and the PNUV of the mycochrome system are membrane-bound and that (b) the transition moment associated with blue light absorption in the presumed flavoprotein forms an angle of at least 53° with the transition moment associated with NUV absorption in PNUV . 相似文献
78.
Isopropylidenation of lactose with 2,2-dimethoxypropane in the presence ofp-toluenesulfonic acid gave two products, which were identified by1H- and13C-NMR as 2,35,63,4-tri-O-isopropylidenelactose dimethyl acetal (1) and its 6-O-(2-methoxy)-isopropyl derivative (2). These products were used for the synthesis of 2-O-methyllactose (7), 2,6-di-O-methyllactose (9) and 2-O-benzyllactose (13). 相似文献
79.
Johan Kumlien Torbjörn Frejd Göran Magnusson David Zopf Arne Lundblad 《Glycoconjugate journal》1986,3(1):85-94
The tetrasaccharide, Glc1-6Glc1-4Glc1-4Glc, denoted (Glc)4, is a limit dextrin formed by amylolytic degradation of glycogen. In order to evaluate the possible clinical importance of (Glc)4 excretion as an indicator of certain physiological and pathological conditions, we have developed a new rapid and inexpensive immunoassay using a monoclonal antibody raised against (Glc)4 glycosidically-linked to a carrier protein. As the antibody is highly specific, it can be used to measure native (Glc)4 directly, without the chemical reduction step required in previous methods. A new type of non-equilibrium ELISA inhibition test was developed based on the capacity of free (Glc)4 to decrease initial rates of antibody binding to (Glc)4-coated microtiter wells. The method is highly reproducible and is as sensitive and accurate as the gas chromatography method or radioimmunoassay used previously.Abbreviations (Glc)4
Glc1-6Glc1-4Glc1-4Glc
- KLH
keyhole limpet hemacyanin
- BSA
bovine serum albumin
- PEG
polyethylene glycol 相似文献