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311.
Narrow groove-like excavations on ammonoid and coiled nautiloid shells are rare in Upper Carboniferous units from Texas, USA. The morphological characteristics of the excavation grooves typically are confined to the ventral and ventrolateral parts of the outer whorl of the shell, are narrower than the length, and have irregular edges where small segments or chips of shells have been removed. Analysis of these features reveals a statistically significant preferential occurrence on ammonoids (1.195% of ca. 3515 specimens) as compared to coiled nautiloids (0.506% of ca. 2965 specimens). The ammonoids typically have longer excavations that penetrate the phragmocone more frequently than those observed in the coiled nautiloids. The groove-like excavations were probably formed by the removal and peeling of shell material by one or more predatory or scavenging arthropods to obtain organic material (tissue and membranes) within the ammonoid and nautiloid body chambers and phragmocones. The excavations probably occurred when the cephalopod was alive (i.e., the cause of death) or shortly after the cephalopod's death. There is no evidence that the excavations are related to sheltering by the excavating organism. 相似文献
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Nisar Ahmad Wani 《Reproductive biology》2021,21(1):100471
Camels are a fundamental livestock resource with a significant role in the agricultural economy of dry regions of Asia and Africa. Similarly, llamas and alpacas are an indigenous resource considered as beasts of burden in South America because of their surefootedness and ability to adapt. Camel racing, a highly lucrative and well-organized sport, camel beauty contests, and high demand for camel milk lead to a steady interest in the multiplication of elite animals by in vitro embryo production (IVEP) in this species during the last few decades. Although offspring have been produced from in vitro produced embryos, the technique is still not that well developed compared with other domestic animal species such as cattle. IVEP involves many steps, including the collection of oocytes from either slaughterhouse ovaries or live animals through ultrasound-guided transvaginal aspiration; in vitro maturation of these collected oocytes; collection and preparation of semen for fertilization; culture and passaging of cells for nuclear transfer, chemical activation of the reconstructed embryos, and in vitro culture of embryos up to the blastocyst stage for transfer into synchronized recipients to carry them to term. This review discusses the present status of all these steps involved in the IVEP of camelids and their future perspectives. 相似文献
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Ishfaq Ahmad Wani Susheel Verma Shazia Mushtaq Abdulaziz Abdullah Alsahli Mohammed Nasser Alyemeni Mohd Tariq Shreekar Pant 《Saudi Journal of Biological Sciences》2021,28(4):2109-2122
The natural populations of Dactylorhiza hatagirea have been greatly affected due to incessant exploitation. As such, studies on its population attributes together with habitat suitability and environmental factors affecting its distribution are needed to be undertaken for its conservation in nature. Present study aimed at accessing an impact of anthropogenic pressure on population structure and locate suitable habitats for the conservation of this critically endangered orchid. Considerable changes in the phytosociological attributes were observed on account of the changing magnitude and extent of anthropogenic threat in their natural abode. The distribution pattern of species indicated that more than 90% of the populations exhibit substantially aggregated spatial distribution. Maximum Entropy (MaxEnt) distribution modelling algorithm was used to predict suitable habitat and potential area for its cultivation and reintroduction. Twenty-seven occurrence records, nineteen bioclimatic variables, altitude, and slope were used. MaxEnt map output gave the habitat suitability for this species and predicted its distribution in the North-Western Himalayas of India for approximately 616 km2. Jackknifing indicated that maximum temperature of warmest month, annual mean temperature, mean temperature of the driest quarter, and mean temperature of the wettest quarter were the governing factors for its distribution and hence, presented a higher gain with respect to other variables. According to permutation importance, precipitation seasonality and mean temperature of wettest quarter shows the prominent impact on the habitat distribution. Results of AUC (area under curve) were statistically significant (0.940) and the line of predicted omission falls very close to an omission on training samples, validating a better run of the model. Response curves revealed a probable increase in the occurrence of D. hatagirea with an increase in mean temperature of the wettest quarter and maximum temperature of the warmest month contributed more than 50% to predicted habitat suitability. Direct field observations concurrent with predicted habitat suitability and google-earth images represent greater model thresholds for successful inception of the species. Together, the study proposes that the species can be conserved in or near its present-day natural habitats and is equally effective in determining the possible habitats for its cultivation and reintroduction. 相似文献
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To assess the role of DNA alkylation damage in oncogene activation, plasmid DNA containing H-ras proto-oncogene (p220-EC) and oncogene (p220-EJ) were treated with increasing concentrations of carcinogenic methylnitrosourea (MNU) and ethylnitrosourea (ENU). The modified plasmid DNA were analyzed by transfection-transformation of the NIH/3T3-recipient cells. Treatment with varying doses of MNU (0.1-5 mM) and ENU (1-15 mM) did not result in the inactivation of the plasmid containing target genes. A transformation efficiency of greater than 40% was observed upon treatment of H-ras oncogene with the highest doses of the alkylating agents. The morphologically transformed foci obtained with alkylated p220-EC ranged from 2.8 to 0.3/microgram MNU alkylated and 1.6 to 0.6/microgram ENU alkylated plasmid DNA. A significant proportion of the morphological transformants exhibited growth in soft agar. The HpaII/MspI restriction length polymorphism (RFLP) at codon 12 of H-ras exon-1 was detected with 4 independently isolated clones obtained from MNU-alkylated p220-EC transfections. Allele-specific in situ gel hybridization with a battery of codon 12 and codon 61 oligonucleotide probes confirmed these RFLPs to be due to sequence changes at codon 12. No clone with sequence changes in the H-ras codon 61 could be detected. The data indicate that a high degree of in vitro alkylation damage of the target gene is necessary to elicit mutational activation of H-ras in transfection-transformation assay. Low frequency notwithstanding, the data demonstrate that DNA alkylation damage at critical target sites can initiate neoplastic cellular transformation. 相似文献
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Summary The screening of micro-organisms decomposing wheat straw was done under laboratory conditions on the basis of the amount of
carbon mineralized from wheat straw during a period of four months. In general, inoculation of wheat straw with different
micro-organisms had favorable effect on the amount of carbon mineralized. Among the bacterial and fungus cultures isolated
from baited wheat straw an Aspergillus sp. (Isolate No. 18) proved to be the most rapid wheat straw decomposer under laboratory conditions. re]19751008 相似文献
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