全文获取类型
收费全文 | 4826篇 |
免费 | 589篇 |
国内免费 | 485篇 |
出版年
2024年 | 10篇 |
2023年 | 155篇 |
2022年 | 191篇 |
2021年 | 186篇 |
2020年 | 249篇 |
2019年 | 293篇 |
2018年 | 241篇 |
2017年 | 242篇 |
2016年 | 257篇 |
2015年 | 282篇 |
2014年 | 285篇 |
2013年 | 604篇 |
2012年 | 284篇 |
2011年 | 329篇 |
2010年 | 293篇 |
2009年 | 284篇 |
2008年 | 245篇 |
2007年 | 233篇 |
2006年 | 219篇 |
2005年 | 185篇 |
2004年 | 175篇 |
2003年 | 125篇 |
2002年 | 104篇 |
2001年 | 68篇 |
2000年 | 57篇 |
1999年 | 41篇 |
1998年 | 31篇 |
1997年 | 29篇 |
1996年 | 20篇 |
1995年 | 18篇 |
1994年 | 24篇 |
1993年 | 13篇 |
1992年 | 26篇 |
1991年 | 7篇 |
1990年 | 15篇 |
1989年 | 10篇 |
1988年 | 13篇 |
1987年 | 4篇 |
1986年 | 9篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1983年 | 6篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1980年 | 6篇 |
1979年 | 8篇 |
1978年 | 5篇 |
1977年 | 2篇 |
1975年 | 1篇 |
1974年 | 2篇 |
排序方式: 共有5900条查询结果,搜索用时 421 毫秒
11.
《Bioscience, biotechnology, and biochemistry》2013,77(12):2762-2765
Comparative two-dimensional electrophoresis showed six proteins, which were significantly produced in the root of salt-tolerant barley. These proteins were identified as stress/defense-related proteins that do not scavenge reactive oxygen species directly, suggesting that salt-tolerant barley develops not only an antioxidative system, but also physical and biochemical changes to cope with salt stress. 相似文献
12.
Aim Species capable of vigorous growth under a wide range of environmental conditions should have a higher chance of becoming invasive after introduction into new regions. High performance across environments can be achieved either by constitutively expressed traits that allow for high resource uptake under different environmental conditions or by adaptive plasticity of traits. Here we test whether invasive and non‐invasive species differ in presumably adaptive plasticity. Location Europe (for native species); the rest of the world and North America in particular (for alien species). Methods We selected 14 congeneric pairs of European herbaceous species that have all been introduced elsewhere. One species of each pair is highly invasive elsewhere in the world, particularly so in North America, whereas the other species has not become invasive or has spread only to a limited degree. We grew native plant material of the 28 species under shaded and non‐shaded conditions in a common garden experiment, and measured biomass production and morphological traits that are frequently related to shade tolerance and avoidance. Results Invasive species had higher shoot–root ratios, tended to have longer leaf‐blades, and produced more biomass than congeneric non‐invasive species both under shaded and non‐shaded conditions. Plants responded to shading by increasing shoot–root ratios and specific leaf area. Surprisingly, these shade‐induced responses, which are widely considered to be adaptive, did not differ between invasive and non‐invasive species. Main conclusions We conclude that high biomass production across different light environments pre‐adapts species to become invasive, and that this is not mediated by plasticities of the morphological traits that we measured. 相似文献
13.
The effect of pretransplant inoculation with VA mycorrhizal fungi on the subsequent growth of leeks in the field 总被引:1,自引:1,他引:0
Summary Leek plants were preinoculated with a mixed inoculum ofGlomus caledonium, Glomus fasciculatum andGlomus sp., and transplanted to Dazomet disinfected and untreated field plots of moderate P deficiency. Successive harvests were
made until 99 days after transplanting. Preinoculated leeks attained marketable weights 25 days earlier than uninoculated
leeks from untreated soil and their final dry matter yields were 5.7 and 1.5 times as high as those of uninoculated leeks
from disinfected and untreated soil, respectively. Phosphorus concentration in preinoculated leeks remained highest for at
least 22 and 75 days after transplanting in untreated and disinfected soil, respectively. Preinoculation had a similar, although
smaller, influence on Cu and Zn concentrations. Infection levels produced by introduced and indigenous VA endophytes in leeks
reached plateaus of 90% and 40%, respectively, 47 days after transplanting. It is concluded that VAM is essential to leeks
grown in moderately P deficient soils, and the potential for inoculating seedlings in commercial leek production is discussed. 相似文献
14.
A note on a semiparametric estimator of mortality 总被引:1,自引:0,他引:1
15.
Gwendolyn L. Waring 《Ecological Research》1988,3(3):205-216
The effects of watering and fertilizer treatments on the vigor and biochemistry of the willow,Salix lasiolepis, and subsequent colonization and survivorship of its gallforming herbivore,Euura lasiolepsis, were investigated in two field experiments. Some plants received low (LW), intermediate (MW) or high (HW) levels of water
as treatments, while others received no (OF), low (LF) or high (HF) fertilizer levels. In the watering experiment, plant protein
concentrations decreased, while growth rate and number of galls per plant increased with increased water treatments. Plant
growth proved to be the best correlate of sawfly attack. Sawfly survivorship increased slightly with greater watering, and
phenol concentrations showed no pattern among treatments. In the fertilization experiment, leaf protein increased with fertilization,
although shoot length, number of galls and survivorship ofE. lasiolepis survivorship were greatest in intermediate treatment plants. In both experiments, plant growth, rather than protein or phenol
levels, was the best predictor of sawfly attack and survivorship.
In a natural experiment with galls on wild plants, galled tissue had significantly greater protein concentrations and lower
phenol concentrations than did ungalled tissue. We suggest that gallformers modify host plant biochemistry within willow galls,
which may explain why the chemical parameters of ambient plant quality we tested were less predictive than plant growth. 相似文献
16.
Kenji Kato Su-wan Oh Hiroyuki Yamamoto Takayuki Hanazato Ikuko Yasuda Akira Otuki Masayuki Takahashi 《Ecological Research》1992,7(3):267-276
In order to understand the control mechanisms of a large, stable bacterial standing stock, enclosure experiments were conducted
in a eutrophic lake, where both bacterial productivity and grazing pressure were very high. Total bacterial number in the
different enclosures ranged from 1.2 to 2.7×107 cells mL−1 throughout the experiment. The average bacterial cell production rate estimated from a grazer eliminating experiment was
6.3×105 cells mL−1 h−1. Difference in the bacterial cell production rate between shaded and unshaded enclosures was not apparent. Bacteria showed
a reduction in standing stock of only about 25–30% even after the supply of light was cut to 1%. Bacteria in the shaded enclosures
then recovered their production rate in the first 12 days of perturbation. Grazing pressure in the shaded enclosures was not
less than that for the control. Thus, it was considered a control mechanism of bacterial stable standing stock that the bacteria
shifted their organic substrate from extracellular dissolved organic carbon freshly released from phytoplankton to that already
stocked in the water column, though it is not known whether the dominant bacteria were the same. 相似文献
17.
V. P. Shabaev 《Plant and Soil》1986,91(2):249-256
Summary Fertilizer/soil N balance of cropped and fallow soil has been studied in a pot experiment carried out with grey forest soil (southern part of Moscow region) at increasing rates of15N labelled ammonium sulfate (0; 8; 16; 32 mg N/100 g of soil). The fertilizer15N balance has been shown to depend upon its application rate and the presence of growing plants. Fertilizer N uptake efficiency was maximum (72.5%) and gaseous losses-minimum (12.5%) at the application rate of 16 mg N/100 g of soil. Fertilizer N losses from the fallow soil were 130–220% versus those from the cropped soil. At the application of fertilizer N the plant uptake of soil N was 170–240% and the amount of soil N as N–NH4 exchangeable + N–NO3 in fallow was 350–440% as compared to the control treatment without nitrogen (PK).After cropping without or with N fertilizer application at the rates of 8 and 32 mg N/100 g of soil, a positive nitrogen balance has been found which is likely due to nonsymbiotic (associative) N-fixation. It has been shown that biologically fixed nitrogen contributes to plant nutrition. 相似文献
18.
19.
Parthenogenesis in Tubificidae 总被引:2,自引:2,他引:0
Tamara L. Poddubnaya 《Hydrobiologia》1984,115(1):97-99
The ability of tubificids to reproduce parthenogenetically following or in place of bisexual reproduction has been proved. During parthenogenesis the spermatogenesis ceases at an early stage of sexual cell development, which, together with some peculiarities of the structure of the sexual system, rules out the possibility of self-fertilization in the worms. For two years of cultivation the life cycles of 3 parthenogenetic generations in Tubifex tubifex and 2 in Limnodrilus hoffmeisteri were traced. 相似文献
20.