全文获取类型
收费全文 | 607篇 |
免费 | 25篇 |
国内免费 | 2篇 |
专业分类
林业 | 46篇 |
农学 | 7篇 |
基础科学 | 1篇 |
72篇 | |
综合类 | 273篇 |
农作物 | 10篇 |
水产渔业 | 50篇 |
畜牧兽医 | 143篇 |
园艺 | 13篇 |
植物保护 | 19篇 |
出版年
2023年 | 5篇 |
2022年 | 6篇 |
2021年 | 5篇 |
2020年 | 14篇 |
2019年 | 19篇 |
2018年 | 13篇 |
2017年 | 17篇 |
2016年 | 4篇 |
2015年 | 6篇 |
2014年 | 12篇 |
2013年 | 24篇 |
2012年 | 51篇 |
2011年 | 61篇 |
2010年 | 24篇 |
2009年 | 18篇 |
2008年 | 40篇 |
2007年 | 55篇 |
2006年 | 53篇 |
2005年 | 39篇 |
2004年 | 40篇 |
2003年 | 39篇 |
2002年 | 33篇 |
2001年 | 7篇 |
2000年 | 1篇 |
1999年 | 3篇 |
1998年 | 2篇 |
1997年 | 2篇 |
1995年 | 3篇 |
1994年 | 3篇 |
1993年 | 3篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 4篇 |
1988年 | 5篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1981年 | 3篇 |
1979年 | 2篇 |
1978年 | 4篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 3篇 |
1967年 | 1篇 |
排序方式: 共有634条查询结果,搜索用时 31 毫秒
591.
592.
Marion I. Menzel Ana‐Maria Oros‐Peusquens Andreas Pohlmeier N. Jon Shah Ulrich Schurr Heike U. Schneider 《植物养料与土壤学杂志》2007,170(1):24-38
Nuclear magnetic resonance imaging (MRI) and complementary analytical techniques were used to address the question whether white asparagus (Asparagus officinalis L.) from different cultivation sites in Germany can be distinguished on the basis of NMR relaxation times. Five locations with contrasting soil properties and composition within the two asparagus‐cultivation regions Rhineland and Lower Franconia were selected for this project. For the first time, entire asparagus plants in their authentic soil environment excavated directly from the original harvest site were imaged by the NMR technique. However, they could not be employed for determination of relaxation times of spears in situ, because of artifacts arising from soil properties. Instead, market‐ready asparagus spears and freshly prepared spear saps from the five locations were used to acquire MRI data sets with different (slow and fast) imaging methods and to compute spatially resolved distributions (maps) of T1, T2, and T2* relaxation times. Comparison of the data for pith, vascular tissue, and peel of the spears yielded only marginal, if any, differences in T1, T2, and T2* between the specimens from the five locations, which were not sufficient for an unambiguous region‐related distinction. More pronounced differences in T1, T2, and T2* were visible for the spear saps, allowing a clear distinction between individual specimens for each of the two cultivation regions. The results are discussed in terms of an application potential for correlated NMR relaxation times of tissue saps for future geographic authentication of agricultural produces. 相似文献
593.
We report the first population ecology study of the endangered Chinese grouse (Bonasa sewerzowi). The study population was stable during 1995-2000. Annual rates of survival were 0.64 for adults and only 0.17 for chicks to 13 weeks of age. Reproductive parameters were 6.1 eggs/clutch, 63% nest success, and overall 3.6 chicks hatched/female/year. The spring sex ratio was 64% males, with 44% of the males unmated in spring. Local people found an estimated 10-29% of the nests and took the eggs for food. Only about 9% of the reserve containing the study area is mature mixed forest, the preferred habitat. Inadequate brood habitat may have influenced chick survival and the skewed adult sex ratio may be a result of habitat fragmentation. We recommend protecting the remaining mixed forest, creating more brood habitat, and stopping the taking of eggs. 相似文献
594.
Jon Zabalza David Ogulei Philip K. Hopke Jong Hoon Lee Injo Hwang Xavier Querol Andrés Alastuey Jesús M. Santamaría 《Water, air, and soil pollution》2006,174(1-4):385-404
Ambient concentrations of PM10 were measured every fifteen minutes from November 2002 to October 2003 at Alsasua (Northern Spain) using a laser particle counter. A high volume sampler was also used to collect 24-h integrated PM10 samples at a frequency of three running days per week (i.e. three consecutive PM10 samples followed by five days without sampling) for gravimetric determination of PM10 mass concentrations followed by chemical analysis of its chemical components. The annual mean PM10 concentration obtained using the laser particle counter with gravimetric correction was 22.7 μg m?3 (365 days), while the mean for the gravimetric samples was 29.5 μg m?3 (134 days). A total of 94 integrated PM10 samples were analyzed for 60 chemical species using a combination of inductively coupled plasma spectrometry (ICP) and ion chromatography (IC). The concentrations of the main PM10 components were found to be generally in agreement with the values reported for other Spanish cities. Bilinear Positive Matrix Factorization (PMF2) was used to study the sources of PM10 and its constituents. Six main sources of PM10 were identified (average contribution to total PM10 mass in parentheses): crustal material (35%), secondary sulfate (21%), secondary nitrate (14%), motor vehicles (12%), sea-salt aerosol (12%) and metallurgical industries (3%). 相似文献
595.
Anna Brzezinska-Paudyn Jon C. Van Loon Maryagnes R. Balicki 《Water, air, and soil pollution》1986,27(1-2):45-56
Inductively coupled plasma atomic emission spectrometry. (ICP-AES), graphite furnace atomic absorption (GFAAS) and gas chromatography with an atomic absorption detector (GC-AAS) were used for the analysis of atmospheric samples collected in the Toronto area of Southern Ontario. Airborne particulate matter and particulate and soluble fractions of snow were analyzed for S, Al, Fe, Ca, Mg, P, Pb, Zn, Cu, Cr, Cd, Ni, As, and Hg. Also, determinations of organic Hg compounds in filtered snow were performed. The element concentrations in airborne particulate matter from Toronto were similar in amount to those found in other major cities and were the highest in winter. Regional differences in the chemical composition of snow were shown to be related to industrial density. The majority of elements existed in the highest concentrations in the soluble fraction of snow, except for Al, Fe, and Pb, which were largely present in particulate matter. Differences in the distribution of elements in particulate matter in fresh and old snow were observed and depended on particle size and element. The results demonstrated the usefulness of snow as an indicator of atmospheric pollution. 相似文献
596.
597.
Alexandra D. Syphard Jon E. Keeley Teresa J. Brennan 《Forest Ecology and Management》2011,261(11):2038-2048
Fuel treatment of wildland vegetation is the primary approach advocated for mitigating fire risk at the wildland-urban interface (WUI), but little systematic research has been conducted to understand what role fuel treatments play in controlling large fires, which factors influence this role, or how the role of fuel treatments may vary over space and time. We assembled a spatial database of fuel breaks and fires from the last 30 years in four southern California national forests to better understand which factors are consistently important for fuel breaks in the control of large fires. We also explored which landscape features influence where fires and fuel breaks are most likely to intersect. The relative importance of significant factors explaining fuel break outcome and number of fire and fuel break intersections varied among the forests, which reflects high levels of regional landscape diversity. Nevertheless, several factors were consistently important across all the forests. In general, fuel breaks played an important role in controlling large fires only when they facilitated fire management, primarily by providing access for firefighting activities. Fire weather and fuel break maintenance were also consistently important. Models and maps predicting where fuel breaks and fires are most likely to intersect performed well in the regions where the models were developed, but these models did not extend well to other regions, reflecting how the environmental controls of fire regimes vary even within a single ecoregion. Nevertheless, similar mapping methods could be adopted in different landscapes to help with strategic location of fuel breaks. Strategic location of fuel breaks should also account for access points near communities, where fire protection is most important. 相似文献
598.
599.
600.
Cohen J 《Science (New York, N.Y.)》2011,333(6047):1216-1218