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131.
Elizabeth M. Hartgers G.H. Aalderink Paul J. Van den Brink Ronald Gylstra J. Wilfred F. Wiegman Theo C.M. Brock 《Aquatic Ecology》1998,32(2):135-152
Twelve indoor, plankton-dominated, freshwater microcosms (600 l) were used to study the effect of a mixture of herbicides
on structural and functional aspects of these ecosystems. The EC50, 72 h values of the most susceptible standard test alga
Selenastrum capricornutum (EC50, atrazine=54 μg l−1, EC50, diuron=15 μg l−1, EC50, metolachlor=56 μg l−1) were used as a starting
point for the dosage applied in the microcosms (dosages: 0, 0.01, 0.03, 0.1, 0.3, 1× EC50). The microcosms were exposed to
chronic levels for 28 days and subsequently monitored for 4 more weeks.
The following effects were observed: (1) direct effects became apparent from an initial drop in photosynthesis efficiency,
pH and oxygen concentration and a decrease in the abundance of several phytoplankton taxa at the 0.3 × EC50 treatment level
and higher. (2) Fourteen days post application an increase in the abundance of several phytoplankton taxa (Chlamydomonas sp.
and Stephanodiscus/Cyclotella) was observed; oxygen concentrations recovered while alkalinity, conductivity and total inorganic
nitrogen were elevated. (3) Effects on fauna were minor. Daphnia galeata showed a decreasing trend and the cyclopoid copepods
an increasing trend at the end of the experiment.
Multivariate statistical analyses demonstrated no effects of any treatment level on the zooplankton community. Effects were
reported for the phytoplankton community at dose levels of 0.3 × EC50 and higher. On species level the most sensitive taxon
was Chlorophyceae coccales. For this taxon a NOEC at the dose level of 0.01 × EC50 was calculated. This effect however was
relatively small in magnitude and merely based on an increase in numbers in the control and lowest treated microcosms rather
than a decrease in numbers in all other treatments. The standards based on algal toxicity data, as adopted by the Uniform
Principles, consist of a safety factors of 0.1 to be multiplied with the EC50. The NOEC of coccales was lower than 0.1 × EC50.
All other observed variables in this aquatic ecosystem were sufficiently protected against the mixture of herbicides by the
safety factor as proposed in the Uniform Principles.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
132.
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134.
Cédric Mabille Damien Pas Markus Aretz Frédéric Boulvain Stephan Schröder Anne-Christine da Silva 《Facies》2008,54(4):597-612
This study focuses on the base of the Eifelian stage and on the abandoned Ohlesberg quarry. The exposed section (92 m thick)
is related to the Lauch and Nohn formations. Petrographic study leads to the definition of 11 microfacies which are integrated
in a palaeogeographical model. It corresponds to a complex ramp setting where carbonate, mixed and siliciclastic deposits
coexist. The microfacies evolution is interpreted in terms of bathymetric and lateral variations, showing a general shallowing-upward
trend and transitions between carbonate-dominated and siliciclastic-dominated sedimentary domains. This interpretation is
supported by trends in magnetic susceptibility data. Even if the proximity to emerged areas appears to be the major influence
on magnetic susceptibility values, the influence of carbonate productivity and wave agitation is also noted. The Ohlesberg
section clearly points to the local and regional complex facies architecture, and advocates to variegated depositional environments
along the Mid-Eifelian High. 相似文献
135.
Diversity of plants in cocoa agroforests in the humid forest zone of Southern Cameroon 总被引:2,自引:1,他引:2
Denis J. Sonwa Bernard A. Nkongmeneck Stephan F. Weise Maturin Tchatat Akin A. Adesina Marc J. J. Janssens 《Biodiversity and Conservation》2007,16(8):2385-2400
In the humid forest zone of Southern Cameroon, farmers generally associate cocoa with native and exotic trees in complex agroforestry
systems. Despite the socio-economic and ecological importance of these systems, few studies have investigated their plant
composition. We investigated tree composition of cocoa agroforests along a gradient of market access, population density and
resource use intensity in the humid forest zone of southern Cameroon, comprising (i) the sub-region of Yaoundé, (ii) the sub-region
of Mbalmayo, and (iii) the sub-region of Ebolowa. Market access, population density and resource use intensity all decreased
from the first to the third sub-region. We quantified the diversity of tree species associated with cocoa within individual
agroforests, among agroforests in the same region, and among the three sub-regions, and classified the tree species according
to their main uses. A total of 9.1 ha belonging to 60 cocoa agroforests were inventoried in 12 villages. We encountered a
total of 206 tree species with an average of 21 tree species per agroforest. In the more urbanized area around Yaoundé, agroforests
were less diverse than in the other sub-regions. In all of the agroforests, food producing tree species tended to be more
frequent than other species. Two thirds of the food trees were native forest species and one third was introduced. From Ebolowa
to Yaoundé, the density of food producing trees doubled and the density of exotic food-producing species increased relative
to native species. Some local species producing high-value non-timber forest products were found in the agroforests, but their
density was far lower than that of exotic tree species. The agroforests also provide medicine, charcoal and other products
for household consumption and sale. We conclude that unless there are specific efforts to promote local forest tree species
in cocoa agroforests, these will progressively lose importance with increasing market access, population pressure and land
use intensity. 相似文献
136.
van der Toorn M Slebos DJ de Bruin HG Leuvenink HG Bakker SJ Gans RO Koëter GH van Oosterhout AJ Kauffman HF 《American journal of physiology. Lung cellular and molecular physiology》2007,292(5):L1211-L1218
Increased lung cell apoptosis and necrosis occur in patients with chronic obstructive pulmonary disease (COPD). Mitochondria are crucially involved in the regulation of these cell death processes. Cigarette smoke is the main risk factor for development of COPD. We hypothesized that cigarette smoke disturbs mitochondrial function, thereby decreasing the capacity of mitochondria for ATP synthesis, leading to cellular necrosis. This hypothesis was tested in both human bronchial epithelial cells and isolated mitochondria. Cigarette smoke extract exposure resulted in a dose-dependent inhibition of complex I and II activities. This inhibition was accompanied by decreases in mitochondrial membrane potential, mitochondrial oxygen consumption, and production of ATP. Cigarette smoke extract abolished the staurosporin-induced caspase-3 and -7 activities and induced a switch from epithelial cell apoptosis into necrosis. Cigarette smoke induced mitochondrial dysfunction, with compounds of cigarette smoke acting as blocking agents of the mitochondrial respiratory chain; loss of ATP generation leading to cellular necrosis instead of apoptosis is a new pathophysiological concept of COPD development. 相似文献
137.
Wim A. Ozinga Stephan M. Hennekens Joop H.J. Schamine Nina A.C. Smits Rene M. Bekker Christine Rmermann Leo Klime Jan P. Bakker Jan M. van Groenendael 《植被学杂志》2007,18(4):489-497
Questions: 1. Which plant traits and habitat characteristics best explain local above‐ground persistence of vascular plant species and 2. Is there a trade‐off between local above‐ground persistence and the ability for seed dispersal and below‐ground persistence in the soil seed bank? Locations: 845 long‐term permanent plots in terrestrial habitats across the Netherlands. Methods: We analysed the local above‐ground persistence of vascular plants in permanent plots (monitored once a year for ca. 16 year) with respect to functional traits and habitat preferences using survival statistics (Kaplan‐Meier analysis and Cox’ regression). These methods account for censored data and are rarely used in vegetation ecology. Results: Local above‐ground persistence is determined by both functional traits (especially the ability to form long‐lived clonal connections) and habitat preferences (especially nutrient requirements). Above‐ground persistence is negatively related to the ability for dispersal by wind and to the ability to accumulate a long‐term persistent soil seed bank (‘dispersal through time’) and is positively related to the ability for dispersal by water. Conclusions: Most species have a half‐life expectation over 15 years, which may contribute to time lags after changes in habitat quality or ‐configuration (‘extinction debt’). There is evidence for a trade‐off relationship between local above‐ground persistence and below‐ground seed persistence, while the relationship with dispersal in space is vector specific. The rate of species turnover increases with productivity. 相似文献
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139.
The amoeba Dictyostelium discoideum is a well-established model organism for studying numerous aspects of cellular and developmental functions. Its rather small (~34Mb) chromosomal genome and the high efficiency of gene disruption by homologous recombination have enabled researchers to dissect various specific gene functions. We describe here the use of one-step cloning for the fast and efficient generation of deletion vectors that are produced in a one-step reaction by inserting two PCR products into an organism-specific, generic acceptor system. This worked efficiently for all 16 tested constructs directed against genes in the amoeba Dictyostelium discoideum. Saving cost and time, the used protocol represents a significant advancement in the generation of such plasmids compared to the conventionally applied restriction enzyme/ligation approach. Using appropriate selection markers, similar systems could also be useful in other organisms, where genes can be knocked out by homologous recombination. 相似文献
140.