全文获取类型
收费全文 | 849篇 |
免费 | 19篇 |
国内免费 | 38篇 |
出版年
2023年 | 7篇 |
2022年 | 5篇 |
2021年 | 11篇 |
2020年 | 15篇 |
2019年 | 15篇 |
2018年 | 22篇 |
2017年 | 22篇 |
2016年 | 19篇 |
2015年 | 21篇 |
2014年 | 31篇 |
2013年 | 53篇 |
2012年 | 17篇 |
2011年 | 46篇 |
2010年 | 25篇 |
2009年 | 52篇 |
2008年 | 45篇 |
2007年 | 57篇 |
2006年 | 43篇 |
2005年 | 32篇 |
2004年 | 23篇 |
2003年 | 25篇 |
2002年 | 14篇 |
2001年 | 15篇 |
2000年 | 21篇 |
1999年 | 25篇 |
1998年 | 14篇 |
1997年 | 19篇 |
1996年 | 17篇 |
1995年 | 21篇 |
1994年 | 18篇 |
1993年 | 11篇 |
1992年 | 20篇 |
1991年 | 15篇 |
1990年 | 20篇 |
1989年 | 17篇 |
1988年 | 16篇 |
1987年 | 10篇 |
1986年 | 8篇 |
1985年 | 7篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 6篇 |
1981年 | 2篇 |
1980年 | 4篇 |
1979年 | 6篇 |
1978年 | 1篇 |
1977年 | 3篇 |
1976年 | 1篇 |
排序方式: 共有906条查询结果,搜索用时 531 毫秒
821.
板栗和锥栗天然同域居群的叶表型变异研究 总被引:2,自引:0,他引:2
对分布于湖北省秭归县境内的一个由169株板栗(Castanea mollissima)和281株锥栗(C.henryi)组成的天然同域居群的20个叶表型性状的变异进行了研究。根据叶片背面和叶柄的被毛情况及叶缘形状3个定性性状,在总共450个个体中,共得到18个(4%)中间过渡类型个体。利用17个数量性状进行逐步判别分析(SDA)表明:根据定性性状得到的中间型个体中分别有7个和11个被归入板栗和锥栗;板栗和锥栗在叶形上的差异较大,有8个数量性状被选入判别方程,判别方程对板栗和锥栗的判别准确率都达93%以上,判别结果较为理想;综合20个表型性状进行主成分分析(PCA),构建了3个主成分,主成分1和2的贡献率分别为53.5%和18.7%,累计贡献率达72.2%。前2个主成分的散布图中,有6个(1/3)中间型个体位于板栗和锥栗的重叠分布区域,可能是二者之间存在杂交的表型证据。 相似文献
822.
本试验以毒死蜱污染土壤为研究材料,利用降解菌DSP-A分别与高丹草、紫花苜蓿、多花黑麦草进行联合修复,探讨了植物-微生物联合修复毒死蜱污染土壤的效果,以及影响联合修复的因素,结果表明,植物.微生物联合修复的效果优于单一的植物修复及单一的微生物修复效果。与DSP—A菌群较合适的植物是高丹草,该组合对毒死蜱的降解率达到96.44%,其次是多花黑麦草。研究了微生物数量、植株密度以及土壤湿度对联合修复效果的影响,结果表明,DSP.A菌菌液稀释倍数越大,联合修复的效果越差。植株密度对联合修复的影响,主要表现为对植物根系生长的影响。植株密度越大,对生存环境的竞争越激烈,植物根系的生长越不好。除了紫花苜蓿外,高丹草和多花黑麦草根系的生长均受到影响。高丹草种植密度为12株/盆时,与DSP—A菌的联合修复效果最好,多花黑麦草则为10株/盆。土壤湿度是影响联合修复的重要因素,不仅影响植物的生长,对微生物的生长也有影响。土壤湿度过大,造成土壤的含氧量降低,不利于植物根系和好氧细菌的生长,从而影响土壤中农药的降解。土壤湿度过小,容易造成植株缺水,根系生长和微生物的生长。高丹草与DSP.A菌、多花黑麦草与DSP—A菌联合修复最适浇水量都为20mL/d,紫花苜蓿与DSP—A菌联合修复最适浇水量都为15mL/d。 相似文献
823.
Dahai Gao Qian Gao Hai-Yan Xu Fei Ma Chang-Ming Zhao Jian-Quan Liu 《Trees - Structure and Function》2009,23(4):717-728
Pinus densata is a homoploid hybrid species, originating from P. tabuliformis × P. yunnanensis. The physiological fitness of this natural hybrid compared to its two parental species remains unknown. In this study, we
investigated physiological responses of the three species by exposing artificially breed seedlings of each to drought stress
lasting 28 days. Our results suggest that, in all three species, drought affected the contents of the plants’ chlorophyll,
stomatal conductance, TBARS, hydrogen peroxide, and free proline and increased the activities of antioxidant enzymes, including
superoxide dismutase (SOD; EC 1.15.1.1), catalase (CAT; EC 1.11.1.6), and peroxidase (POD; EC 1.11.1.7). The drought stress
also induced significant changes in the activity of ascorbate peroxidase (APX; EC 1.11.1.11), monodehydroascorbate reductase
(MDHAR; EC 1.6.5.4), dehydroascorbate reductase (DHAR; EC 1.8.5.1), glutathione reductase (GR; EC 1.6.4.2), and levels of
ascorbate and glutathione in the ascorbate–glutathione cycle. The hybrid species P. densata appeared to achieve greater drought tolerance and exhibit hybrid superiority in antioxidant processes and other related physiological
traits compared to the two parental species, although a few of the hybrid’s measured variables were similar to those of P. tabuliformis. However, P. yunnanensis was more sensitive to drought and appeared to have the lowest resistance to such stress. These physiological differences
are largely consistent with the species’ habitat preferences, which may reflect their early genetic divergences and niche
differentiation. These findings provide important information for management and forest restoration efforts of these species
in the future. 相似文献
824.
Jong-Hwan Eun Ji-Ho Son Jeong-Min Moon Jong-Shik Chung 《The International Journal of Life Cycle Assessment》2009,14(4):364-373
Background, aim, and scope As the sustainability improvement becomes an essential business task of industry, a number of companies are adopting IT-based
environmental information systems (EIS). Life cycle assessment (LCA), a tool to improve environmental friendliness of a product,
can also be systemized as a part of the EIS. This paper presents a case of an environmental information system which is integrated
with online LCA tool to produce sets of hybrid life cycle inventory and examine its usefulness in the field application of
the environmental management.
Main features Samsung SDI Ltd., the producer of display panels, has launched an EIS called Sustainability Management Initiative System (SMIS).
The system comprised modules of functions such as environmental management system (EMS), green procurement (GP), customer
relation (e-VOC), eco-design, and LCA. The LCA module adopted the hybrid LCA methodology in the sense that it combines process
LCA for the site processes and input–output (IO) LCA for upstream processes to produce cradle-to-gate LCA results. LCA results
from the module are compared with results of other LCA studies made by the application of different methodologies. The advantages
and application of the LCA system are also discussed in light of the electronics industry.
Results and discussion LCA can play a vital role in sustainability management by finding environmental burden of products in their life cycle. It
is especially true in the case of the electronics industry, since the electronic products have some critical public concerns
in the use and end-of-life phase. SMIS shows a method for hybrid LCA through online data communication with EMS and GP module.
The integration of IT-based hybrid LCA in environmental information system was set to begin in January 2006. The advantage
of the comparing and regular monitoring of the LCA value is that it improves the system completeness and increases the reliability
of LCA. By comparing the hybrid LCA and process LCA in the cradle-to-gate stage, the gap between both methods of the 42-in.
standard definition plasma display panel (PDP) ranges from 1% (acidification impact category) to −282% (abiotic resource depletion
impact category), with an average gap of 68.63%. The gaps of the impact categories of acidification (AP), eutrophication (EP),
and global warming (GWP) are relatively low (less than 10%). In the result of the comparative analysis, the strength of correlation
of three impact categories (AP, EP, GWP) shows that it is reliable to use the hybrid LCA when assessing the environmental
impacts of the PDP module. Hybrid LCA has its own risk on data accuracy. However, the risk is affordable when it comes to
the comparative LCA among different models of similar product line of a company. In the results of 2 years of monitoring of
42-in. Standard definition PDP, the hybrid LCA score has been decreased by 30%. The system also efficiently shortens man-days
for LCA study per product. This fact can facilitate the eco-design of the products and can give quick response to the customer's
inquiry on the product's eco-profile. Even though there is the necessity for improvement of process data currently available,
the hybrid LCA provides insight into the assessments of the eco-efficiency of the manufacturing process and the environmental
impacts of a product.
Conclusions and recommendations As the environmental concerns of the industries increase, the need for environmental data management also increases. LCA shall
be a core part of the environmental information system by which the environmental performances of products can be controlled.
Hybrid type of LCA is effective in controlling the usual eco-profile of the products in a company. For an industry, in particular
electronics, which imports a broad band of raw material and parts, hybrid LCA is more practicable than the classic LCA. Continuous
efforts are needed to align input data and keep conformity, which reduces data uncertainty of the system. 相似文献
825.
Host preferences in both sexes of Pseudacteon tricuspis Borgmeier (Jaguariuna biotype) and Pseudacteon curvatus Borgmeier (Formosa biotype) and their relative attraction to the imported fire ants (IFA), Solenopsis invicta Buren (red IFA), Solenopsis richteri Forel (black IFA) and S. invicta × S. richteri hybrids (hybrid IFA) were investigated in two separate experiments utilizing multiple choice flight bioassays. The results of both experiments clearly showed that both sexes of the Jaguariuna biotype of P. tricuspis could distinguish among the three IFA species and demonstrated greater preference for hybrid IFA and red IFA. This conclusion is supported by a variety of data collected on the number of fly visits, attack rate, and hovering duration (Experiment 1), and on the number of trapped flies (Experiment 2), which showed that black IFA is the least preferred of the three species. Similar results were recorded for the Formosan biotype of P. curvatus, although the data were not as strongly conclusive. Females of this biotype spent a significantly greater amount of time in hovering mode over red IFA and hybrid IFA compared to black IFA, but the other data were not significant. The red IFA is the natural host of both phorid fly biotypes and our results suggest that both biotypes may have evolved a specialized relationship with red IFA including an ability to discriminate it from related fire ants. These results are discussed in relation to the possible role of fire ant chemicals in mediating host preferences in phorid flies, contributions of male phorid flies to fire ant biocontrol, and the practical implications of the key findings. 相似文献
826.
Daniel R. Matute Jerry A. Coyne 《Evolution; international journal of organic evolution》2010,64(4):903-920
Drosophila santomea and D. yakuba are sister species that live on the volcanic African island of São Tomé. Previous work has revealed several barriers to gene flow, including sexual isolation, hybrid sterility, and “extrinsic” ecological isolation based on differential adaptation to and preference for temperature. Here, we describe several new “intrinsic” barriers to gene flow—barriers that do not depend on the species’ ecology. These include reduced egg number, reduced egg hatchability, and faster depletion of sperm in interspecific compared to intraspecific matings. Further, hatching interval and egg‐to‐adult development time are significantly longer in interspecific than intraspecific crosses. If a female of either species is initially mated to a heterospecific male, she lays fewer and less‐fertile eggs than if she is first mated to a conspecific male, so that heterospecific matings permanently reduce female fertility. Finally, D. santomea females mated to D. yakuba males do not live as long as virgin or conspecifically mated females. The “poisoning” effects of heterospecific ejaculates may be byproducts of antagonistic sexual selection. Although these species diverged relatively recently, they are clearly separated by many isolating barriers that act both before and after mating. 相似文献
827.
Masayuki Takamiya Noriko Ohta Chika Fujimaru-Takaoka Khota Uki 《Journal of plant research》2000,113(2):203-215
Diplazium with summer-green bi- to tripinnate leaves. Diplazium mesosorum and D. sibiricum var. sibiricum are sexual diploids (2n=82; n=41ll); D. chinense and D. squamigerum are sexual tetraploids (2n=164; n=82ll); and D. sibiricum var. glabrum is a sterile triploid (2n=123; meiosis irregular). Diplazium nipponicum includes both sterile triploid and sexual tetraploid populations. The triploid is larger in relation to several morphological
characteristics and occurs in more southern regions than the tetraploid. Allozyme analysis suggests that the triploid is a
hybrid of recurrent origin between the tetraploid and an unknown diploid. Diplazium × bittyuense is a sterile tetraploid, and the mitotic chromosome number, meiotic chromosome behavior, and allozyme analysis confirm the
working hypothesis that it is a hybrid between D. nipponicum and D. chinense. Apomicts are not found within Diplazium with summer-green bi- to tripinnate leaves, and the taxonomic complexity can be attributed to polyploidy and natural hybridization.
Received 3 March 2000/ Accepted in revised form 19 April 2000 相似文献
828.
829.
杂交水稻苗瘟抗性的配合力和遗传力分析 总被引:3,自引:0,他引:3
采用7×7不完全双列杂交设计,对反映杂交水稻苗瘟抗性的5个指标进行了配合力和遗传力分析.结果表明,杂交水稻苗瘟抗性遗传力高,受加性和非加性基因效应共同控制,但以加性效应为主;恢复系的苗瘟抗性一般配合力效应明显相对重要于不育系,不育系苗瘟抗性一般配合力效应对F1代的抗性有显著的影响;14个供试亲本中,多恢1号、成恢149、K42A、K40A具有较好的苗瘟抗性一般配合力效应.因此,在杂交水稻抗苗瘟育种中,对恢复系的抗性GCA选择和对亲本的抗性GCA评鉴至关重要,但不应忽视不育系对组合的抗性贡献和对组合的抗性评鉴;多恢1号、成恢149、K42A和K40A可作为优良抗苗瘟亲本加以利用. 相似文献
830.
利用显微操作仪将小鼠精子注入家兔卵母细胞的胞质内和透明带下,对鼠兔异种精卵互作和异种受精胚胎的发育进行了研究,并对注射精子的数量及卵的体外成熟时间等影响鼠兔异种显微受精的因素进行了探讨,结果如下:(1)将小鼠精子分别注入兔卵胞质内和透明带下,均能激活兔卵母细胞,导致精核解聚和原核形成;(2)小鼠精子注入兔卵胞质内和透明带下受精,杂种胚胎体外培养能发育到8-细胞期;(3)鼠兔异种受精4-细胞胚胎染色体标本制备观察结果表明,它们为正常二倍体;(4)鼠兔异种受精4-细胞胚胎的超微结构观察结果表明,它们极近似兔正常4-细胞胚胎的超微结构;(5)将小鼠精子注入兔卵透明带下,注射5—10个精子组卵的受精率(32.4%)和卵裂率(16.2%)均高于注射单个精子组的,但二组间差异不显著(P>0.05);DM 15%NCS液中体外成熟培养11—12h兔卵透明带下注入1—2个小鼠精子后的受精率(42.3%)和卵裂率(30.8%)均高于体外成熟培养24—25h组的,但二组间差异未达到显著水平(P>0.05)。 相似文献