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111.
Comparative study of two meromictic basins of Lake Banyoles (Spain) with sulphur phototrophic bacteria 总被引:1,自引:1,他引:0
The annual limnological dynamics of two meromictic basins of Lake Banyoles (C-III and C-IV) have been studied and compared
on the basis of their physical, chemical and biological characters. Stability values calculated for both basins gave 865 g
cm cm−2 and 495 g cm cm−2 for C-III and C-IV respectively. These values are in agreement with the fact that C-IV was almost completely mixed during
winter. In this basin, during stratification, the monimolimnion increased in thickness as the stability increased. Isolation
of the respective monimolimnia resulted in the development of anoxic conditions and the accumulation of sulphide in both C-III
and C-IV, which favoured the development of dense populations of sulfur phototrophic bacteria. The purple sulphur bacterium
Chromatium minus and the green sulphur bacterium Chlorobium phaeobacteroides were identified as the main components of these photosynthetic populations. The different depths at which the O2/H2S boundary was situated in both basins (and consequently the different light intensity reaching this zone) determined the
growth of these bacteria. Light intensities at the chemocline of C-IV reached values up to 5% of surface incident light. In
contrast, in C-III this variable was sensibly lower, with values depending on season and seldom reaching 1%. Phototrophic
bacteria were consequently found earlier in C-IV than in C-III, where no significant concentrations were found until August.
Finally stability is discussed as an important factor controlling chemical and biological dynamics in meromictic lakes. 相似文献
112.
Effects of eucalyptus afforestation on leaf litter dynamics and macroinvertebrate community structure of streams in Central Portugal 总被引:3,自引:3,他引:0
To test the hypothesis whether afforestation with Eucalyptus globulus affects litter dynamics in streams and the structure of macroinvertebrate aquatic communities, we compared streams flowing through eucalyptus and deciduous forests, paying attention to: (i) litterfall dynamics, (ii) accumulation of organic matter, (iii) processing rates of two dominant leaf species: eucalyptus and chestnut, and (iv) macroinvertebrate community structure. The amount of allochthonous inputs was similar in both vegetation types, but the seasonality of litter inputs differed between eucalyptus and natural deciduous forests. Eucalyptus forest streams accumulated more organic matter than deciduous forest streams. Decomposition of both eucalyptus and chestnut leaf litter was higher in streams flowing through deciduous forests. The eucalyptus forest soils were highly hydrophobic resulting in strong seasonal fluctuations in discharge. In autumn the communities of benthic macroinvertebrates of the two stream types were significantly different. Deciduous forest streams contained higher numbers of invertebrates and more taxa than eucalyptus forest streams. Mixed forest streams (streams flowing through eucalyptus forests but bordered by deciduous vegetation) were intermediate between the two other vegetation types in all studied characteristics (accumulation of benthic organic matter, density and diversity of aquatic invertebrates). These results suggest that monocultures of eucalyptus affect low order stream communities. However, the impact may be attenuated if riparian corridors of original vegetation are kept in plantation forestry. 相似文献
113.
The possibility of ecosystem boundary changes in northern Brazilian Amazonia during the Holocene period was investigated using soil organic carbon isotope ratios. Determination of past and present fluctuations of the forest-savanna boundary involved the measurement of natural 13C isotope abundance, expressed as 13C, in soil organic matter (SOM). SOM 13C analyses and radiocarbon dating of charcoal fragments were carried out on samples derived from soil profiles taken along transects perpendicular to the ecotonal boundary. SOM 13C values in the upper soil horizons appeared to be in equilibrium with the overlying vegetation types and did not point to a movement of the boundary during the last decades. However, 13C values obtained from deeper savanna and forest soil layers indicated that the vegetation type has changed in the past. In current savanna soil profiles, we observed the presence of mid-Holocene charcoals derived from forest species: fire frequency at that time was probably greater, and more extensive savanna may have resulted. Isotope data and the presence of these charcoals thus suggest that the forest-savanna boundary has shifted significantly in the recent Holocene period, forest being more extensive during the early Holocene than today. During the middle Holocene, the forest could have strongly regressed, and fires appeared, with a maximum development of the savanna vegetation. At the beginning of the late Holocene, the forest may have invaded a part of this savanna, and fires occurred again. 相似文献
114.
C. Sauvain-Dugerdil G. Boëtsch C. Serrano-Sanchez 《International Journal of Anthropology》1996,11(2-4):3-11
this first paper introduces the topic of the volume, outcomes of a symposium organised at the 13th ICAES held in Mexico in
August 1993. It briefly reminds of the convergence between anthropology and demography up to date and stresses on the need
of real transdisciplinary work in this challenging domain. The aim of the symposium was to make a contribution on the central
theme chosen by the congress — the cultural and biological dimensions of global change — while examining the place of demographic
anthropology in the study of change. The papers presented at the symposium have been organised in three parts which form the
present volume: the composition of population, the choice of spouse and mobility, the reproduction and dynamics of populations.
The basic mechanisms of change are considered through examples at the level of local populations. This also leads to question
the definitions of human groups and to make a “declaration” stressing on the importance of individual heterogeneity and the
arbitrariness and reductive nature of any grouping of individuals, stating therefore the misapprehension of the most recent
scientific work inherent to the rationale of programs of “ethnic cleasing”.
Translated from the french by prof. Derek F. Roberts 相似文献
115.
华北棉区夏播棉田害虫发生特点分析 总被引:4,自引:1,他引:3
分析和比较了华北棉区夏季播种与春季播种的棉田主要害虫(棉铃虫与棉蚜)的发生特点,探讨了它们的管理对策。 相似文献
116.
根据Fuzzy数学原理和三化螟生物学特性,组建了四代三化螟发生动态综合预测模型经对福建省将乐县16年四代三化螟发生期、发生量回报及1995年的预报,拟合率及正确率均达100%。 相似文献
117.
The MC dynamics of an off-lattice all-atom protein backbone model with rigid amide planes are studied. The only degrees of freedom are the dihedral angle pairs of the C-atoms. Conformational changes are generated by Monte Carlo (MC) moves. The MC moves considered are single rotations (simple moves, SM's) giving rise to global conformational changes or, alternatively, cooperative rotations in a window of amide planes (window moves, WM's) generating local conformational changes in the window. Outside the window the protein conformation is kept invariant by constraints. These constraints produce a bias in the distribution of dihedral angles. The WM's are corrected for this bias by suitable Jacobians. The energy function used is derived from the CHARMM force field. In a first application to polyalanine it is demonstrated that WM's sample the conformational space more efficiently than SM's.Abbreviations CPU
Central Processing Unit
- MC
Monte Carlo
- MCD
Monte Carlo Dynamics
- MD
Molecular Dynamics
- RMS
Root-Mean-Square
- RMSD
Root-Mean-Square-Deviation
- SM
Simple Move
- WM
Window Move 相似文献
118.
K. W. Wolf 《Protoplasma》1996,191(3-4):148-157
Summary Kinetochore structure was examined in metaphase spermatogonia and primary spermatocytes of the red firebug,Pyrrhocoris apterus (Pyrrhocoridae, Hemiptera). Chromosome spreads were analysed using light microscopy and serial sections through spindles were studied using electron microscopy. Mitotic chromosomes were rod-shaped bodies and did not possess primary constrictions. Trilaminar kinetochores occurred throughout about 72% of the chromosomal length. Numerous microtubules (MTs) were connected with the outer plates of the kinetochores and interactions between MTs and the remainder of the chromosomal surface were rare. The bivalents formed dumbbell-shaped bodies in metaphase I spermatocytes. At that stage, MTs were found in contact with the entire poleward surface of the chromosomes. Distinct kinetochore material was, however, not detectable and some MTs penetrated deeply into the chromatin. Mitotic and meiotic chromosomes ofP. apterus are holokinetic and consequently the number of kinetochore MTs is expected to be relatively high. In the second part of the study, the question whether holokinetic chromosomes affect spindle MT dynamics is addressed. To this end, primary spermatocytes ofP. apterus were labelled with a widely used antibody, 6-11B-1, directed against acetylated -tubulin. The acetylation of -tubulin is believed to indicate the presence of long-lived MTs. MT bundles were labelled in metaphase and anaphase I spindles, while prophase and prometaphase I spermatocytes did not contain acetylated MTs. MTs in early and mid telophase spindles were not acetylated. Only late telophase I spindles possessed small amounts of acetylated -tubulin. The acetylated MT bundles of metaphase and anaphase I spindles probably represent kinetochore MTs stabilized by their association with the holokinetic chromosomes at one end and the spindle poles at the opposite end.Abbreviations BSA
bovine serum albumin
- DAPI
4,6-diamidino-2-phenylindole · 2HCl
- EGTA
ethylene glycol-bis (-aminoethyl ether)-N,N-tetraacetic acid
- FITC
fluorescein-isothiocyanate
- PBS
phosphate-buffered saline
- PIPES
piperazine-N,N bis(2-ethane sulfonic acid)
- MT
microtubule 相似文献
119.
Evolution takes place in an ecological setting that typically involves interactions with other organisms. To describe such
evolution, a structure is needed which incorporates the simultaneous evolution of interacting species. Here a formal framework
for this purpose is suggested, extending from the microscopic interactions between individuals – the immediate cause of natural
selection, through the mesoscopic population dynamics responsible for driving the replacement of one mutant phenotype by another,
to the macroscopic process of phenotypic evolution arising from many such substitutions. The process of coevolution that results
from this is illustrated in the context of predator–prey systems. With no more than qualitative information about the evolutionary
dynamics, some basic properties of predator–prey coevolution become evident. More detailed understanding requires specification
of an evolutionary dynamic; two models for this purpose are outlined, one from our own research on a stochastic process of
mutation and selection and the other from quantitative genetics. Much of the interest in coevolution has been to characterize
the properties of fixed points at which there is no further phenotypic evolution. Stability analysis of the fixed points of
evolutionary dynamical systems is reviewed and leads to conclusions about the asymptotic states of evolution rather different
from those of game-theoretic methods. These differences become especially important when evolution involves more than one
species.
Received 10 November 1993; received in revised form 25 July 1994 相似文献
120.
Impact of initial density of cowpea aphid Aphis craccivora Koch (Aphididae) at infestation on the growth and yield of aphid-susceptible cowpea cultivar ICV-1 and aphid-resistant cultivar ICV-12, was investigated. Plants at the seedling, flowering and podding stages of development were infested with five aphid densities consisting of 0, 2, 5, 10 and. 20 aphids per plant and maintained for 22 days. Extended leaf heights of plants and aphid counts were recorded at 7, 12, 17 and 22 days after infestation. Two crop growth parameters (biomass duration and leaf area duration), and two plant yield parameters (number of pods per plant and number of seeds per pod) were recorded. Due to the occurrence of parthenogenesis and changes in population dynamics during infestations, aphid densities were converted into cumulative cowpea aphid-days, to facilitate data analyses and interpretation. ANOVA indicated that there was significant (P=s 0.05) difference in aphid-day accumulations between the two cultivars when infested at the seedling stage. Accumulations on cv. ICV-1 were greater than on cv. ICV-12. However, no such differences between the cultivars were detected when plants were infested at flowering and podding stages. Therefore, the seedling stage was used for comparisons of the impact of cowpea aphid-days on the growth and yield parameters of the two cultivars. At the 95% confidence intervals, ICV-12 plants were consistently taller than ICV-1 plants. Infested ICV-1 seedlings showed stunting and other growth deformities which were not observed on ICV-12 plants. Regression analyses revealed substantial reductions in the growth and yield parameters of ICV-1 relative to ICV-12. Overall, cowpea aphid-days provided a convenient and reliable method for studying the aphid population dynamics and the subsequent impact on plant growth and yield performance. 相似文献